Our Research

Current state of industrial heating and opportunities for decarbonization

The IPCC recommends keeping the global average temperature increase well below 2 °C, if not below 1.5 °C, by 2100 to avoid the worst effects of climate change. This requires achieving carbon neutrality shortly after 2050. In the United States, industrial emissions represent 22% of greenhouse gas emissions and are particularly hard to decarbonize, because (1) the processes emit CO2 as a byproduct of chemical reactions and (2) these industries require high-grade heat input. This study focuses on some of these industries, namely cement, lime, glass, and steelmaking. This work details the incumbent kiln and furnace technologies and explores the developing processes with examples of existing projects that aim to reduce carbon emissions, such as carbon capture and storage (CCS), fuel switching, and other technological changes.

An overview of the status and challenges of CO2 storage in minerals and geological formations

Since the Industrial Revolution, anthropogenic carbon dioxide (CO2) emissions have grown exponentially, accumulating in the atmosphere and leading to global warming. According to the IPCC (IPCC Special Report 2018), atmospheric warming should be less than 2 ℃ to avoid the most serious consequences associated with climate change. This goal can be achieved in part by reducing CO2 emissions, together with capturing and sequestering CO2 from point sources. The most mature storage technique is sequestration in deep saline aquifers. In addition, CO2 can be mineralized and sequestered in solid form by various techniques: ex-situ, surficial and in situ mineralization. Ex situ and surficial approaches may produce valuable products while mitigating environmental hazards. In-situ mineralization uses ultramafic and mafic geological formations for permanent, solid storage. A portfolio that limits warming to less than 2 ℃ by 2100 will include avoiding CO2 emissions and removal of CO2 from air. Regardless of the specific mix of approaches, it will be essential to permanently sequester tens of billions of tons of CO2. Maximizing the potential of all of these storage technologies will help to meet global climate goals. The research agenda published by the National Academy of Science (NASEM 2019) calls for about $1 billion over a 10-20 year time period to advance deployment of CO2 sequestration in deep sedimentary reservoirs at the GtCO2/yr scale and develop CO2 mineralization at the MtCO2/yr scale.

Getting to neutral: options for negative carbon emissions in California

This report is an assessment of negative emissions pathways—ones that physically remove CO 2 from the atmosphere—that can help California achieve carbon neutrality by 2045, or sooner. It integrates original research findings with current published research on three main pillars of negative emissions: natural and working lands, carbon capture from biomass conversion to fuels, and direct air capture. The focus and scope of this report is unique: it only addresses practices and technologies for removing carbon dioxide from the air. It also encompasses the entire breadth of strategies, from land management to the latest technological options, and it evaluates the cost of every step of the solution, from waste biomass collection to carbon dioxide transport and geologic storage. The methods are intended to be transparent; details of the calculations and underlying data are included in the report body and appendices. This study intentionally avoids any discussion of policies and does not include current incentives; it provides a range of options, tradeoffs and costs that can be used to inform future policies. The key finding of this report is that carbon neutrality is achievable.

Negative emissions technologies and reliable sequestration: A research agenda

To achieve goals for climate and economic growth," negative emissions technologies"(NETs) that remove and sequester carbon dioxide from the air will need to play a significant role in mitigating climate change. Unlike carbon capture and storage technologies that remove carbon dioxide emissions directly from large point sources such as coal power plants, NETs remove carbon dioxide directly from the atmosphere or enhance natural carbon sinks. Storing the carbon dioxide from NETs has the same impact on the atmosphere and climate as simultaneously preventing an equal amount of carbon dioxide from being emitted. Recent analyses found that deploying NETs may be less expensive and less disruptive than reducing some emissions, such as a substantial portion of agricultural and land-use emissions and some transportation emissions. In 2015, the National Academies published Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration, which described and initially assessed NETs and sequestration technologies. This report acknowledged the relative paucity of research on NETs and recommended development of a research agenda that covers all aspects of NETs from fundamental science to full-scale deployment. To address this need, Negative Emissions Technologies and Reliable Sequestration: A Research Agenda assesses the benefits, risks, and" sustainable scale potential" for NETs and sequestration. This report also defines the essential components of a research and development program, including its estimated costs and potential impact.

Hydrogen production via natural gas steam reforming in a Pd-Au membrane reactor. Comparison between methane and natural gas steam reforming reactions

High-purity hydrogen to be fed directly to a PEMFC was produced by carrying out natural gas steam reforming under moderate operating conditions in a Pd-Au composite membrane reactor packed with a commercial Ni-based catalyst. The Pd-Au composite membrane with a thickness of approximately 12 µm was fabricated by using both electroless and electroplating techniques to deposit Pd and Au layers, respectively, over a porous stainless-steel support. After annealing, the membrane showed a hydrogen permeance of 1.30 × 10−3 mol/s-m2-Pa0.5 at 450 °C, and near-infinite ideal selectivity of H2/Ar at pressures lower than 300 kPa and at temperatures lower than 400 °C. The natural gas reforming reaction was performed at 450 °C with a steam-to-methane ratio of 3.5 and gas hourly space velocity of 2600 h−1 at different operating pressures varying from 100 kPa to 300 kPa.

Negative emissions—Part 2: Costs, potentials and side effects

The most recent IPCC assessment has shown an important role for negative emissions technologies (NETs) in limiting global warming to 2 C cost-effectively. However, a bottom-up, systematic, reproducible, and transparent literature assessment of the different options to remove CO 2 from the atmosphere is currently missing.

Negative emissions—Part 1: Research landscape and synthesis

With the Paris Agreement's ambition of limiting climate change to well below 2 C, negative emission technologies (NETs) have moved into the limelight of discussions in climate science and policy. Despite several assessments, the current knowledge on NETs is still diffuse and incomplete, but also growing fast. Here, we synthesize a comprehensive body of NETs literature, using scientometric tools and performing an in-depth assessment of the quantitative and qualitative evidence therein.

Carbon capture and storage (CCS): the way forward

CO2 capture from the industry sector

It is widely accepted that greenhouse gas emissions, especially CO2, must be significantly reduced to prevent catastrophic global warming. Carbon capture and reliable storage (CCS) is one path towards controlling emissions, and serves as a key component to climate change mitigation and will serve as a bridge between the fossil fuel energy of today and the renewable energy of the future. Although fossil-fueled power plants emit the vast majority of stationary CO2, there are many industries that emit purer streams of CO2, which result in reduced cost for separation. Moreover, many industries outside of electricity generation do not have ready alternatives for becoming low-carbon and CCS may be their only option. The thermodynamic minimum work for separation was calculated for a variety of CO2 emissions streams from various industries, followed by a Sherwood analysis of capture cost.

Carbon capture and utilization in the industrial sector

The fabrication and manufacturing processes of industrial commodities such as iron, glass, and cement are carbon-intensive, accounting for 23% of global CO2 emissions. As a climate mitigation strategy, CO2 capture from flue gases of industrial processesmuch like that of the power sectorhas not experienced wide adoption given its high associated costs. However, some industrial processes with relatively high CO2 flue concentration may be viable candidates to cost-competitively supply CO2 for utilization purposes (e.g., polymer manufacturing, etc.). This work develops a methodology that determines the levelized cost ($/tCO2) of separating, compressing, and transporting carbon dioxide. A top-down model determines the cost of separating and compressing CO2 across 18 industrial processes.

Selection of shale preparation protocol and outgas procedures for applications in low-pressure analysis

The low-pressure gas adsorption (LPGA) method for estimation of pore capacities, pore size distributions, and total surface area using adsorption–desorption isotherms is selected as an effective technique in pore characterization. A recent application of this method is to understand the complex and heterogeneous nature of shales across the globe. The LPGA experiments were conducted on shale samples from Barnett and Eagle Ford formations in the United States using CO2 for micropores of 0.3–1.5 nm in diameter and N2 and Ar as the adsorbates to focus on micropores from 1.5 to 2.0 nm and the lower range of mesopores above 2.0–27 nm in diameter. It was hypothesized that a significant error in estimations could occur due to inconsistencies in the shale outgas temperatures.

Methane and CO2 Adsorption Capacities of Kerogen in the Eagle Ford Shale from Molecular Simulation

Over the past decade, the United States has become a world leader in natural gas production, thanks in part to a large-fold increase in recovery from unconventional resources, i.e., shale rock and tight oil reservoirs. In an attempt to help mitigate climate change, these depleted formations are being considered for their long-term CO2 storage potential. Because of the variability in mineral and structural composition from one formation to the next (even within the same region), it is imperative to understand the adsorption behavior of CH4 and CO2 in the context of specific conditions and pore surface chemistry, i.e., relative total organic content (TOC), clay, and surface functionality.

Assessment of reasonable opportunities for direct air capture

This work explores the possibility of using CO 2 captured directly from the atmosphere for several applications that require low to moderate purities. Comparisons of the minimum and real work for separating CO 2 from air, natural gas combined cycle flue gas and pulverized coal combustion flue gas are proposed and discussed. Although it is widely accepted that the separation of CO 2 from air to high purity is more energy-intensive than separating CO 2 from more concentrated sources, this study presents select cases where the separation of CO 2 from air to low and moderate purities is energetically equivalent with the work required for flue gas CO 2 separation. These energetically-competitive cases are shown to be dependent on the percent capture and final CO 2 purity desired.

CO2 Storage and Flow Capacity Measurements on Idealized Shales from Dynamic Breakthrough Experiments

Dynamic column breakthrough (DCB) measurements were carried out on idealized shale samples for the first time, based on a custom-designed system. To better understand the contribution of different shale minerals on flow and storativity, measurements were carried out on composition-controlled shales having known weight percentages of total organic carbon (TOC) and illite. CO2 was assessed for its potential for sequestration, as well as its applicability as a fracturing fluid for enhanced gas recovery in shale formations. Experimental results reveal an increase in permeability and CO2 adsorption with either increasing TOC or illite content. This is attributed to the complex porous structure of kerogen, as well as the interlayering characteristics of clay minerals, resulting in large surface area and pore volume ratios.

Natural gas steam reforming reaction at low temperature and pressure conditions for hydrogen production via Pd/PSS membrane reactor

The objective of this work is to analyze the performance of a composite palladium-based membrane reactor (MR) by performing the natural gas steam reforming reaction at low operating conditions for producing high-purity hydrogen. The MR comprises a composite membrane, having ~13 µm Pd layer deposited on a porous stainless steel support, fabricated via electroless plating and a commercial Ni-based catalyst. The composite membrane shows infinite ideal selectivity, H2/He and H2/Ar, at trans-membrane pressures less than 100 kPa and T=400 °C at the onset of experimental testing. The steam reforming reaction is performed at 400 °C, by varying the reaction pressures and sweep gas flow rate between 150 kPa and 300 kPa, and 0–100 mL/min, respectively. The gas hourly space velocity (GHSV) and steam-to-carbon ratio (S/C) are kept constant at 2600 h−1 and 3.5.

High-performance oxygen reduction and evolution carbon catalysis: From mechanistic studies to device integration

The development of high-performance and low-cost oxygen reduction and evolution catalysts that can be easily integrated into existing devices is crucial for the wide deployment of energy storage systems that utilize O2-H2O chemistries, such as regenerative fuel cells and metal-air batteries. Herein, we report an NH3-activated N-doped hierarchical carbon (NHC) catalyst synthesized via a scalable route, and demonstrate its device integration. The NHC catalyst exhibited good performance for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), as demonstrated by means of electrochemical studies and evaluation when integrated into the oxygen electrode of a regenerative fuel cell. The activities observed for both the ORR and the OER were comparable to those achieved by state-of-the-art Pt and Ir catalysts in alkaline environments. We have further identified the critical role of carbon defects as active sites for electrochemical activity through density functional theory calculations and high-resolution TEM visualization. As a result, this work highlights the potential of NHC to replace commercial precious metals in regenerative fuel cells and possibly metal-air batteries for cost-effective storage of intermittent renewable energy.

Tunable Polyaniline‐Based Porous Carbon with Ultrahigh Surface Area for CO2 Capture at Elevated Pressure

Natural gas is the cleanest fossil fuel source. However, natural gas wells typically contain considerable amounts of CO2, with on‐site CO2 capture necessary. Solid sorbents are advantageous over traditional amine scrubbing due to their relatively low regeneration energies and non‐corrosive nature. However, it remains a challenge to improve the sorbent's CO2 capacity at elevated pressures relevant to natural gas purification. Here, the synthesis of porous carbons derived from a 3D hierarchical nanostructured polymer hydrogel, with simple and effective tunability over the pore size distribution is reported. The optimized surface area reaches 4196 m2 g−1, which is among the highest of carbon‐based materials, with abundant micro‐ and narrow mesopores (2.03 cm3 g−1 with d < 4 nm).

Hierarchical N-Doped Carbon as CO2 Adsorbent with High CO2 Selectivity from Rationally Designed Polypyrrole Precursor

Here, we report the controlled synthesis of a novel N-doped hierarchical carbon that exhibits record-high Henry’s law CO2/N2 selectivity among physisorptive carbons while having a high CO2 adsorption capacity.

Advances on methane steam reforming to produce hydrogen through membrane reactors technology: A review

Methane steam reforming is the most common industrial process used for almost the 50% of the world’s hydrogen production. Commonly, this reaction is performed in fixed bed reactors and several stages are needed for separating hydrogen with the desired purity. The membrane reactors represent a valid alternative to the fixed bed reactors, by combining the reforming reaction for producing hydrogen and its separation in only one stage. This article deals with the recent progress on methane steam reforming reaction, giving a short overview on catalysts utilization as well as on the fundamentals of membrane reactors, also summarizing the relevant advancements in this field.

First-Principles Investigation of Mercury Adsorption on the α-Fe2O3(11̅02) Surface

Theoretical investigations using density functional theory (DFT) have been carried out to understand the interaction between mercury (Hg) and hematite (α-Fe2O3), both of which are released during the coal combustion processes. A clean α-Fe2O3(11̅02) surface was chosen as a representative hematite model in this study based upon a previous ab initio thermodynamics study showing the high stability of this surface in the temperature range of typical flue gases. In order to determine the effect of chlorine (Cl) during Hg adsorption, the most probable adsorption sites of Hg, Cl, and HgCl on the clean α-Fe2O3 surface termination were found based on adsorption energy calculations, and the oxidation states of the adsorbates were determined by Bader charge analysis. Additionally, the projected density of states (PDOS) analysis characterizes the surface–adsorbate bonding mechanism.

Observations and assessment of fly ashes from high-sulfur bituminous coals and blends of high-sulfur bituminous and subbituminous coals: environmental processes recorded at the …

Fly ash was investigated with a variety of chemical, mineralogical, petrographic, and microbeam techniques from three coal-fired units at two Kentucky power plants. Two units burn high-sulfur Illinois Basin high volatile bituminous (hvb) coal, and the third unit burns a ∼70:30 blend of high-sulfur Illinois Basin hvb coal and low-sulfur, relatively high-CaO Powder River Basin subbituminous coal. With high-S, high-Fe coals in all of the blends, spinel (magnetite) is an important constituent in the fly ashes. Overall, the fly ashes are dominated by glass. Portlandite was noted in the high-Ca-coal-derived ash. Concentrations of Ba and Sr are highest in the latter fly ash, a function of the Powder River Basin coal source for a portion of the blend.

Mercury interaction with the fine fraction of coal-combustion fly ash in a simulated coal power plant flue gas stream

Mercury associated with fly ash is a significant contaminant released in flue gas emissions from coal-fired power plants. This work focuses on the association of Hg with other elements and phases as well as the molecular-level speciation of Hg in bulk and <0.1 μm sized fly ash particles reacted with a Hg-containing simulated flue gas stream. Following reaction under conditions chosen to simulate an electrostatic precipitator operating at 140 °C, fly ash (bulk and ≤0.1 μm) from a Kentucky power plant was analyzed using microscopic and spectroscopic techniques. The ≤0.1 μm fraction dominates Hg uptake, with total Hg concentrations increasing from 100 ppb to 610 ppm after reaction, whereas bulk ash concentrations increase from 11 to 164 ppb.

Enhancing Catalytic CO Oxidation over Co3O4 Nanowires by Substituting Co2+ with Cu2+

Co3O4 is an attractive earth-abundant catalyst for CO oxidation, and its high catalytic activity has been attributed to Co3+ cations surrounded by Co2+ ions. Hence, the majority of efforts for enhancing the activity of Co3O4 have been focused on exposing more Co3+ cations on the surface. Herein, we enhance the catalytic activity of Co3O4 by replacing the Co2+ ions in the lattice with Cu2+. Polycrystalline Co3O4 nanowires for which Co2+ is substituted with Cu2+ are synthesized using a modified hydrothermal method. The Cu-substituted Co3O4_Cux polycrystalline nanowires exhibit much higher catalytic activity for CO oxidation than pure Co3O4 polycrystalline nanowires and catalytic activity similar to those single crystalline Co3O4 nanobelts with predominantly exposed most active {110} planes.

Climate intervention: Reflecting sunlight to cool earth

As one of a two-book report, this volume of Climate Intervention discusses albedo modification-changing the fraction of incoming solar radiation that reaches the surface. This approach would deliberately modify the energy budget of Earth to produce a cooling designed to compensate for some of the effects of warming associated with greenhouse gas increases.

Methylene blue adsorption on the basal surfaces of kaolinite: Structure and thermodynamics from quantum and classical molecular simulation

Organic dyes such as methylene blue (MB) are often used in the characterization of clays and related minerals, but details of the adsorption mechanisms of such dyes are only partially understood from spectroscopic data, which indicate the presence of monomers, dimers, and higher aggregates for varying mineral surfaces. A combination of quantum (density functional theory) and classical molecular simulation methods was used to provide molecular detail of such adsorption processes, specifically the adsorption of MB onto kaolinite basal surfaces. Slab models with vacuum-terminated surfaces were used to obtain detailed structural properties and binding energies at both levels of theory, while classical molecular dynamics simulations of aqueous pores were used to characterize MB adsorption at infinite dilution and at higher concentration in which MB dimers and one-dimensional chains formed.

Ultrahigh surface area three-dimensional porous graphitic carbon from conjugated polymeric molecular framework

Porous graphitic carbon is essential for many applications such as energy storage devices, catalysts, and sorbents. However, current graphitic carbons are limited by low conductivity, low surface area, and ineffective pore structure. Here we report a scalable synthesis of porous graphitic carbons using a conjugated polymeric molecular framework as precursor. The multivalent cross-linker and rigid conjugated framework help to maintain micro- and mesoporous structures, while promoting graphitization during carbonization and chemical activation. The above unique design results in a class of highly graphitic carbons at temperature as low as 800 °C with record-high surface area (4073 m2 g–1), large pore volume (2.26 cm–3), and hierarchical pore architecture.

Climate intervention: carbon dioxide removal and reliable sequestration

Advancing adsorption and membrane separation processes for the gigaton carbon capture challenge

Reducing CO2 in the atmosphere and preventing its release from point-source emitters, such as coal and natural gas–fired power plants, is a global challenge measured in gigatons. Capturing CO2 at this scale will require a portfolio of gas-separation technologies to be applied over a range of applications in which the gas mixtures and operating conditions will vary. Chemical scrubbing using absorption is the current state-of-the-art technology. Considerably less attention has been given to other gas-separation technologies, including adsorption and membranes. It will take a range of creative solutions to reduce CO2 at scale, thereby slowing global warming and minimizing its potential negative environmental impacts. This review focuses on the current challenges of adsorption and membrane-separation processes.

Klinkenberg effect on predicting and measuring helium permeability in gas shales

To predict accurately gas-transport in shale systems, it is important to study the transport phenomena of a non-adsorptive gas such as helium to investigate gas “slippage”. Non-equilibrium molecular dynamics (NEMD) simulations have been carried out with an external driving force imposed on the 3-D carbon pore network generated atomistically using the Voronoi tessellation method, representative of the carbon-based kerogen porous structure of shale, to investigate helium transport and predict Klinkenberg parameters. Simulations are conducted to determine the effect of pressure on gas permeability in the pore network structure. In addition, pressure pulse decay experiments have been conducted to measure the helium permeability and Klinkenberg parameters of a shale core plug to establish a comparison between permeability measurements in the laboratory and the permeability predictions using NEMD

Methane leaks from North American natural gas systems

Multiple scientific studies suggest that methane emissions from natural gas systems could be larger than estimated in official inventories, with implications for the use of natural gas in sustainable energy systems.

Mercury chemistry of brominated activated carbons–packed-bed breakthrough experiments

Coal-fired power plants provided between 45% and 50% of the United States net energy generation in the years between 1999 and 2010 and will continue to be a primary source of electricity into the future. Among the major environmental concerns of coal utilization is the release of mercury (Hg), which was recently regulated by the US EPA in the Mercury and Air Toxics Standards (MATS) ruling in December 2011. Among the variety of potential methods for Hg capture, activated carbon injection (ACI) is viewed by the EPA as a viable, ready technology available to energy utilities to comply with MATS. However, there remain significant questions regarding the complicated interaction between the carbon sorbent, Hg, and contaminants present in combustion flue gas, such as SO2 and NOx (NO and NO2).

Molecular simulation and experimental characterization of the nanoporous structures of coal and gas shale

Characterization of coal and shale is required to obtain pore size distribution (PSD) in order to create realistic models to design efficient strategies for carbon capture and sequestration (CCS) at full scale. Proton nuclear magnetic resonance (NMR) cryoporometry and low-pressure gas adsorption isothermal experiments, conducted with N2 at 77 K over a P/P0 range of 10− 7 to 0.995, were carried out to determine the PSD and total pore volumes to provide insight into the development of realistic simulation models for the organic matter comprising coal and gas shale rock. The PSDs determined on the reference materials (SiliaFlash F60 and Vycor 7930) show a reasonable agreement between low-pressure gas adsorption and NMR cryoporometry showing complementarity of the two independent techniques.

Carbon dioxide conversion into hydrocarbon fuels on defective graphene-supported Cu nanoparticles from first principles

Density functional theory studies demonstrate that defective graphene-supported Cu nanoparticles can modify the structural and electronic properties of copper for enhancing electrochemical reduction of carbon dioxide (CO2) into hydrocarbon fuels (CH4, CO, and HCOOH). We not only provide improved understanding of CO2 conversion mechanisms on both Cu and the Cu nanoparticle system, but also explain a key factor for enhanced CO2 conversion.

Sol-flame synthesis of cobalt-doped TiO 2 nanowires with enhanced electrocatalytic activity for oxygen evolution reaction

Doping nanowires (NWs) is of crucial importance for a range of applications due to the unique properties arising from both impurities' incorporation and nanoscale dimensions. However, existing doping methods face the challenge of simultaneous control over the morphology, crystallinity, dopant distribution and concentration at the nanometer scale. Here, we present a controllable and reliable method, which combines versatile solution phase chemistry and rapid flame annealing process (sol-flame), to dope TiO2 NWs with cobalt (Co). The sol-flame doping method not only preserves the morphology and crystallinity of the TiO2 NWs, but also allows fine control over the Co dopant profile by varying the concentration of Co precursor solution. Characterizations of the TiO2:Co NWs show that Co dopants exhibit 2+ oxidation state and substitutionally occupy Ti sites in the TiO2 lattice.

An X-ray photoelectron spectroscopy study of surface changes on brominated and sulfur-treated activated carbon sorbents during mercury capture: performance of pellet versus …

This work explores surface changes and the Hg capture performance of brominated activated carbon (AC) pellets, sulfur-treated AC pellets, and sulfur-treated AC fibers upon exposure to simulated Powder River Basin-fired flue gas. Hg breakthrough curves yielded specific Hg capture amounts by means of the breakthrough shapes and times for the three samples. The brominated AC pellets showed a sharp breakthrough after 170–180 h and a capacity of 585 μg of Hg/g, the sulfur-treated AC pellets exhibited a gradual breakthrough after 80–90 h and a capacity of 661 μg of Hg/g, and the sulfur-treated AC fibers showed no breakthrough even after 1400 h, exhibiting a capacity of >9700 μg of Hg/g.

Role of WO3 in the Hg Oxidation across the V2O5–WO3–TiO2 SCR Catalyst: A DFT Study

Selective catalytic reduction (SCR) units can be exploited to reduce Hg emissions from coal-based power plants; hereby, Hg0 is oxidized into Hg2+, which has a higher solubility than the former and can therefore be scrubbed before leaving the stacks. With the purpose of examining the effect of the surface composition and surface coverage on the reactivity of a commercial SCR catalyst (V2O5–WO3–TiO2) toward Hg oxidation, two models were used to represent TiO2-supported systems with low and high loading of the two active phases (i.e., V2O5 and WO3). The reactivities of these systems were compared through the analysis of the adsorption energies of Hg, Cl•, HgCl, and HCl, which are likely involved in the Hg oxidation mechanism.

Heterogeneous mercury oxidation on Au (111) from first principles

Density functional theory (DFT) studies of mercury oxidation on Au(111) are conducted to determine the potential Hg oxidation mechanisms taking place on catalytic gold surfaces by using the Perdew and Wang approximation (PW91) described by a generalized gradient approximation (GGA). The Hg oxidation was examined via a Langmuir–Hinshelwood mechanism where each Hg0 and Cl2 (or HCl) species is separately adsorbed on the gold surface and the bimolecular reaction occurs through the formation of bound HgCl and HgCl2. For this, the Climbing Image-Nudged Elastic Band (CI-NEB) method has been employed to calculate the activation energies of HgCl and HgCl2 formation pathways. In the three-step Hg oxidation mechanism (Hg → HgCl → HgCl2), the second Cl attachment step is endothermic which is the reaction rate-limiting step, while the first Cl attachment step is exothermic.

CO2 Mitigation Potential of Mineral Carbonation with Industrial Alkalinity Sources in the United States

The availability of industrial alkalinity sources is investigated to determine their potential for the simultaneous capture and sequestration of CO2 from point-source emissions in the United States. Industrial alkalinity sources investigated include fly ash, cement kiln dust, and iron and steel slag. Their feasibility for mineral carbonation is determined by their relative abundance for CO2 reactivity and their proximity to point-source CO2 emissions. In addition, the available aggregate markets are investigated as possible sinks for mineral carbonation products. We show that in the U.S., industrial alkaline byproducts have the potential to mitigate approximately 7.6 Mt CO2/yr, of which 7.0 Mt CO2/yr are CO2 captured through mineral carbonation and 0.6 Mt CO2/yr are CO2 emissions avoided through reuse as synthetic aggregate (replacing sand and gravel).

Molecular simulation of methane adsorption in micro-and mesoporous carbons with applications to coal and gas shale systems

Methane adsorption in porous carbon systems such as coal and the organic matrix of gas shales is an important factor in determining the feasibility of CO2 injection for enhanced natural gas recovery and possible sequestration of CO2. Methane and CO2 adsorb competitively on carbon surfaces and an understanding of each gas individually is important for determining a model to predict the feasibility of this approach for permanent CO2 storage.

Slippage and viscosity predictions in carbon micropores and their influence on CO2 and CH4 transport

Non-equilibrium molecular dynamics simulations of pure carbon dioxide and methane and their equimolar mixtures have been carried out with an external driving force imposed on carbon slit pores to investigate gas slippage and Klinkenberg effects. Simulations were conducted to determine the effect of pore size and exposure to an external potential on the velocity profile and slip-stick boundary conditions. The simulations indicate that molecule-wall collisions influence the velocity profile, which deviates significantly from the Navier-Stokes hydrodynamic prediction for micro- and mesopores. Also, the shape of the velocity profile is found to be independent of the applied pressure gradient in micropores.

DFT study of Hg oxidation across vanadia-titania SCR catalyst under flue gas conditions

The density functional theory was used to analyze the thermodynamic stability and reactivity of the vanadia-titania catalyst below monolayer regime with the purpose of having a good representation of a commercial SCR catalyst (V2O5(<2 wt %)–TiO2). The objective of this paper is to understand the reactivity of this catalyst in Hg oxidation. The SCR catalyst is modeled as a tetrahedrally coordinated divanadate unit supported on a 3-layer TiO2(001) slab to represent a catalyst with low vanadia loadings. Under flue gas conditions, the interaction of water with this surface has been studied as a function of pressure and temperature using ab initio thermodynamic calculations, showing that water coverage is temperature-dependent. Adsorbed water acts as a Lewis base, donating electrons to the TiO2(001) surface support, which increases the negative charge and reactivity of the oxygen atoms of the vanadia dimer.

Molecular Simulation Studies of CO2 Adsorption by Carbon Model Compounds for Carbon Capture and Sequestration Applications

Effects of oxygen-containing surface functionalities on the adsorption of mixtures including CO2/CH4, CO2/N2, and CO2/H2O have been investigated in the current work. Together with Bader charge analysis, electronic structure calculations have provided the initial framework comprising both the geometry and corresponding charge information required to carry out statistical-based molecular simulations. The adsorption isotherms and selectivity of CO2 from CO2/N2, CO2/CH4, and CO2/H2O gas mixtures were determined by grand canonical Monte Carlo simulations at temperature/pressure conditions relevant to carbon capture and sequestration applications. The interactions between the surfaces with induced polarity and nonpolar/polar molecules have been investigated.

Molecular simulation of CO2 adsorption in micro-and mesoporous carbons with surface heterogeneity

To mitigate and stabilize atmospheric CO2 concentrations, alternate energy sources with zero carbon emissions offer ultimate solutions. However, technologies based on efficient and economic generation of electricity from non-carbonized energy sources are still in development. Therefore, carbon capture combined with sequestration as a component of a greater portfolio of solutions to reduce CO2 emissions may be carried out during our transition from fossil-based resources to renewables or non-carbonized resources. As one of the attractive options, CO2 captured by carbon-based sorbents as well as CO2 sequestration in unmineable coalbeds require a thorough understanding of the adsorption properties in micro- and mesoporous carbon materials.

Mercury chemistry on brominated activated carbon

Activated carbon-based sorbents are the most widely tested sorbents for mercury removal in coal-fired power plants. A major problem in mercury removal is the limited understanding of the mechanism associated with elemental mercury (Hg0) oxidation and its subsequent adsorption. This work investigates the possible binding mechanism of Hg0 onto brominated fiber and powder activated carbon sorbents through packed-bed experiments in a stream of air. To better understand the mechanisms involved, a combination of spectroscopy and quantum mechanical modeling were used to characterize the sorption process. X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy were used to analyze the surface and bulk chemical compositions of brominated activated carbon sorbents reacted with Hg0.

Molecular modeling of carbon dioxide transport and storage in porous carbon-based materials

To fundamentally study the molecular processes in porous carbon-based systems relevant to transport and storage of carbon dioxide, non-equilibrium molecular dynamics simulations have been carried out with an external driving force imposed on a carbon-based 3-D pore network. The purpose of this study is to investigate the transport properties of pure carbon dioxide, methane and nitrogen as well as binary mixtures nitrogen and carbon dioxide and also methane and carbon dioxide through modeled 3-D carbon-based systems representative of porous carbon-based materials. The 3-D pore network has been generated atomistically using the Voronoi tessellation method of a structure containing approximately 125,000 atoms.

Investigation of adsorption behavior of mercury on Au (111) from first principles

The structural and electronic properties of Hg, SO2, HgS, and HgO adsorption on Au(111) surfaces have been determined using density functional theory with the generalized gradient approximation. The adsorption strength of Hg on Au(111) increases by a factor of 1.3 (from −9.7 to −12.6 kcal/mol) when the number of surface vacancies increases from 0 to 3; however, the adsorption energy decreases with more than three vacancies. In the case of SO2 adsorption on Au(111), the Au surface atoms are better able to stabilize the SO2 molecule when they are highly undercoordinated. The SO2 adsorption stability is enhanced from −0.8 to −9.3 kcal/mol by increasing the number of vacancies from 0 to 14, with the lowest adsorption energy of −10.2 kcal/mol at 8 Au vacancies. Atomic sulfur and oxygen precovered-Au(111) surfaces lower the Hg stability when Hg adsorbs on the top of S and O atoms.

Carbon capture

The first book on Carbon Capture, written buy our own Jennifer Wilcox.

Mechanisms of the oxygen reduction reaction on defective graphene-supported Pt nanoparticles from first-principles

The mechanisms of the oxygen reduction reaction (ORR) on defective graphene-supported Pt13 nanoparticles have been investigated to understand the effect of defective graphene support on the ORR and predict details of ORR pathways.

Effects of Surface Heterogeneity on the Adsorption of CO2 in Microporous Carbons

Carbon capture combined with utilization and storage has the potential to serve as a near-term option for CO2 emissions reduction. CO2 capture by carbon-based sorbents and CO2 storage in geologic formations such as coal and shale both require a thorough understanding of the CO2 adsorption properties in microporous carbon-based materials. Complex pore structures for natural organic materials, such as coal and gas shale, in addition to general carbon-based porous materials are modeled as a collection of independent, noninterconnected, functionalized graphitic slit pores with surface heterogeneities. Electronic structure calculations coupled with van der Waals-inclusive corrections have been performed to investigate the electronic properties of functionalized graphitic surfaces.

Mercury adsorption and oxidation in coal combustion and gasification processes

This review explores the current state of knowledge associated with the kinetically-limited homogeneous reaction pathways in addition to the complexities associated with heterogeneous oxidation processes.

Impact of alkalinity sources on the life-cycle energy efficiency of mineral carbonation technologies

This study builds a holistic, transparent life cycle assessment model of a variety of aqueous mineral carbonation processes using a hybrid process model and economic input–output life cycle assessment approach (hybrid EIO-LCA). The model allows for the evaluation of the tradeoffs between different reaction enhancement processes while considering the larger lifecycle impacts on energy use and material consumption. A preliminary systematic investigation of the tradeoffs inherent in mineral carbonation processes is conducted to provide guidance for the optimization of the life-cycle energy efficiency of various proposed mineral carbonation processes. The life-cycle assessment of aqueous mineral carbonation suggests that a variety of alkalinity sources and process configurations are capable of net CO2 reductions.

Economic and energetic analysis of capturing CO2 from ambient air

We investigate the thermodynamic efficiencies of commercial separation systems as well as trace gas removal systems to better understand and constrain the energy requirements and costs of these air capture systems. Our empirical analyses of operating commercial processes suggest that the energetic and financial costs of capturing CO2 from the air are likely to have been underestimated.

DFT-based study on oxygen adsorption on defective graphene-supported Pt nanoparticles

The structural and electronic properties of Pt13 nanoparticles adsorbed on monovacancy defective graphene have been determined to understand oxygen adsorption on Pt nanoparticles based upon density functional theory predictions using the generalized gradient approximation. We demonstrate that a monovacancy site of graphene serves a key role as an anchoring point for Pt13 nanoparticles, ensuring their stability on defective graphene surfaces and suggesting their enhanced catalytic activity toward the interaction with O2. Strong hybridization of the Pt13 nanoparticle with the sp2 dangling bonds of neighboring carbon atoms near the monovacancy site leads to the strong binding of the Pt13 nanoparticle on defective graphene (−7.45 eV in adsorption energy).

DFT studies on the interaction of defective graphene-supported Fe and Al nanoparticles

The structural, electronic, and magnetic properties of Fe13 and Al13 nanoparticles adsorbed on monovacancy defective graphene have been determined using density functional theory with the generalized gradient approximation (GGA). Graphene vacancies are used as anchoring points for these pure metal nanoparticles, ensuring their isolated stability on the surface, thereby maximizing their catalytic reactivity through the availability of undercoordinated surface sites along with a high surface area. The results of this work indicate that the strong binding of Fe13 and Al13 nanoparticles on defective graphene (−6.98 and −3.84 eV in adsorption energy, respectively) is due to strong hybridization of the nanoparticles with the sp2 dangling bonds of neighboring carbons near the vacancy.

Heterogeneous mercury reaction chemistry on activated carbon

Experimental and theory-based investigations have been carried out on the oxidation and adsorption mechanism of mercury (Hg) on brominated activated carbon (AC). Air containing parts per billion concentrations of Hg was passed over a packed-bed reactor with varying sorbent materials at 140 and 30 °C. Through X-ray photoelectron spectroscopy surface characterization studies it was found that Hg adsorption is primarily associated with bromine (Br) on the surface, but that it may be possible for surface-bound oxygen (O) to play a role in determining the stability of adsorbed Hg. In addition to surface characterization experiments, the interaction of Hg with brominated AC was studied using plane-wave density functional theory.

CO2 Adsorption on Carbon Models of Organic Constituents of Gas Shale and Coal

Imperfections of the organic matrix in coal and gas shales are modeled using defective and defect-free graphene surfaces to represent the structural heterogeneity and related chemical nature of these complex systems. Based upon previous experimental investigations that have validated the stability and existence of defect sites in graphene, plane-wave electronic density functional theory (DFT) calculations have been performed to investigate the mechanisms of CO2 adsorption. The interactions of CO2 with different surfaces have been compared, and the physisorption energy of CO2 on the defective graphene adsorption site with one carbon atom missing (monovacancy) is approximately 4 times as strong as that on a perfect defect-free graphene surface, specifically, with a physisorption energy of ∼210 meV on the monovacancy site compared to ∼50 meV on a perfect graphene surface.

Direct air capture of CO2 with chemicals: a technology assessment for the APS Panel on Public Affairs

This report explores direct air capture (DAC) of carbon dioxide (CO2) from the atmosphere with chemicals. DAC involves a system in which ambient air flows over a chemical sorbent that selectively removes the CO2. The CO2 is then released as a concentrated stream for disposal or reuse, while the sorbent is regenerated and the CO2-depleted air is returned to the atmosphere.

Investigation of H2 and H2S Adsorption on Niobium- and Copper-Doped Palladium Surfaces

Alloying or doping Pd may be an option for overcoming sulfur poisoning. The current investigation probes the mechanism associated with sulfur binding to determine if Nb and Cu are appropriate doping metals. In this study, the effect of doping Pd with Cu or Nb on the binding strength of H2 and H2S was investigated using plane-wave density functional theory-based electronic structure calculations to determine mechanisms of adsorption. Results of this work indicate that for pure Pd and Pd-doped surfaces, H2 dissociates with the H atoms most stable on the fcc−fcc site. The overall d-band centers calculated for H2 adsorption at the fcc−fcc site for the pure and doped-Pd surfaces indicate that the H2 adsorption strength trend is Pd > Cu > Nb. Regarding H2S adsorption on Pd and Pd-doped surfaces, it was found that Cu has a lower affinity for H2S compared to Pd and Nb.

Mercury capture by native fly ash carbons in coal-fired power plants

The control of mercury in the air emissions from coal-fired power plants is an ongoing challenge. The native unburned carbons in fly ash can capture varying amounts of Hg depending upon the temperature and composition of the flue gas at the air pollution control device, with Hg capture increasing with a decrease in temperature; the amount of carbon in the fly ash, with Hg capture increasing with an increase in carbon; and the form of the carbon and the consequent surface area of the carbon, with Hg capture increasing with an increase in surface area. The latter is influenced by the rank of the feed coal, with carbons derived from the combustion of low-rank coals having a greater surface area than carbons from bituminous- and anthracite-rank coals.

A density functional theory study of the charge state of hydrogen in metal hydrides

Density functional theory and Bader charge analyses were used to investigate the charge state of hydrogen in vanadium, niobium, tantalum, palladium, and niobium−palladium alloys. Over a range of concentrations and hydrogen-site configurations, it is found that hydrogen consistently acquires a net charge of between approximately −0.51e and −0.64e in the pure group 5 metals compared with a significantly smaller value of 0.3e in palladium. Although there is indirect evidence that the electronic charge plays a role in the solubility and diffusivity of hydrogen in the group 5 metals, this is the first work to quantify the value of the charge. Hydrogen tends to migrate to regions of the metal lattice that minimize its overall charge density, which generally corresponds to the T-site in the bcc metals.

Understanding mercury binding on activated carbon

Understanding the mechanism by which mercury adsorbs on activated carbon is crucial to the design and fabrication of effective capture technologies. In this study, the possible binding mechanism of mercury (Hg) and its species, i.e., HgCl and HgCl2 on activated carbon is investigated using ab initio-based energetic calculations. The activated carbon surface is modeled by a single graphene layer in which the edge atoms on the upper side are unsaturated in order to simulate the active sites. In some cases, chlorine atoms are placed at the edge sites to examine the effect of chlorine on the binding of Hg, HgCl and HgCl2. It has been concluded that both HgCl and HgCl2 can be adsorbed dissociatively or non-dissociatively. In the case of dissociative adsorption, it is energetically favorable for atomic Hg to desorb and energetically favorable for it to remain on the surface in the Hg1+ state, HgCl.

A kinetic investigation of high-temperature mercury oxidation by chlorine

First-stage mercury oxidation reactions typical of coal combustion flue gases were investigated. The present study is a determination of the kinetic and thermodynamic parameters of the bimolecular reactions, Hg + Cl2 ↔ HgCl + Cl, Hg + HCl ↔ HgCl + H, and Hg + HOCl ↔ HgCl + OH, at the B3LYP/RCEP60 VDZ level of theory over a temperature range of 298.15 to 2000 K at atmospheric pressure. Conventional transition state theory was used to predict the forward and reverse rate constants for each reaction and ab initio based equilibrium constant expressions were calculated as a function of temperature. Reasonable agreement was achieved between the calculated equilibrium constants and the available experimental values.

Hg binding on Pd binary alloys and overlays

The vast majority of the mercury released from coal combustion is elemental mercury. Noble metals such as Pd, Au, Ag, and Cu have been proposed to capture elemental mercury. Density functional theory calculations are carried out to investigate mercury interactions with Pd binary alloys and overlays in addition to pure Pd, Au, Ag, and Cu surfaces using a projected augmented wave method with the Perdew−Wang generalized gradient approximation. It has been determined that Pd has the highest mercury binding energy in comparison to other noble metals. In addition, Pd is found to be the primary surface atom responsible for improving the interaction of mercury with the surface atoms in both Pd binary alloys and overlays. Deposition of Pd overlays on Au and Ag enhance the reactivity of the surface by shifting the d-states of surface atoms up in energy.

Mercury Species and SO2 Adsorption on CaO(100)

First principles-based quantum mechanical tools based upon Density Functional Theory were used to investigate the binding mechanism of Hg species and SO2 on CaO(100) surfaces for parallel and perpendicular orientations. One-fold, 2-fold and 3-fold high symmetry adsorption sites have been examined for the species, Hg0, SO2, HgCl, HgCl2 and HgO. It has been discovered that HgCl, HgCl2, and SO2 are strongly adsorbed on the CaO(100) surface at 0.125 ML coverage with chemisorption as the likely adsorption mechanism.

Mercury adsorption on PdAu, PdAg and PdCu alloys

Under specific conditions, sorbent materials such as activated carbon, metal oxides, metal sulfides and pure metals can effectively capture mercury (Hg). Among these materials activated carbon is one of the most widely-used sorbents because of its high removal capacity. Unfortunately, activated carbon can hinder the recycling of particulate matter for concrete manufacturing because it prevents concrete from meeting the freeze-thaw requirements. The use of a sorbent material that can capture Hg efficiently but is also concrete-friendly would allow for the increased sale of waste materials, ultimately oversetting landfill costs. In this work, density functional theory calculations have been used to predict the binding mechanism of Hg on the binary alloys PdAu(111), PdAg(111), PdCu(111) which are potential candidates for concrete-friendly sorbents.

Mercury binding on activated carbon

Density functional theory has been employed for the modeling of activated carbon (AC) using a fused‐benzene ring cluster approach. Oxygen functional groups have been investigated for their promotion of effective elemental mercury binding on AC surface sites. Lactone and carbonyl functional groups yield the highest mercury binding energies. Further, the addition of halogen atoms has been considered to the modeled surface, and has been found to increase the AC's mercury adsorption capacity. The mercury binding energies increase with the addition of the following halogen atoms, F > Cl > Br > I, with the fluorine addition being the most promising halogen for increasing mercury adsorption.

Solubility of hydrogen in PdAg and PdAu binary alloys using density functional theory

The present work deals with the study of palladium-silver (PdAg) and palladium-gold (PdAu) binary alloys over a broad range of temperatures and alloy compositions using density functional theory (DFT) to find possible conditions where the solubility of hydrogen (H) is significantly higher than that of pure palladium (Pd). Several alloy structures, such as Pd100-xAgx with x = 14.81, 25.93, 37.04, and 48.51, Pd100-xAux with x = 14.81, 25.93, and 37.04, and Pd100-xCux with x = 25.93 and 48.51 were considered. The lattice constants of these structures were optimized using DFT, and relaxed structures were used for the estimation of binding energy. It was found that the solubility of H in PdAg is higher than pure Pd with a maximum at approximately 30% Ag at 456 K. Also, the solubility of PdAu alloys was higher than pure Pd with a maximum at about 20% Au with a solubility 12 times higher than that of pure Pd.

Achieving optimum hydrogen permeability in PdAg and PdAu alloys

The present work investigates both the diffusivity and permeability of hydrogen (H) in palladium-silver (PdAg) and palladium-gold (PdAu) alloys over a 400–1200K temperature range for Pd100−XMX, M=Ag or Au and X=0%–48% using density functional theory (DFT) and kinetic Monte Carlo simulations (KMC). DFT has been employed to obtain octahedral (O)-, tetrahedral (T)-, and transition state (TS)- site energetics as a function of local alloy composition for several PdAg and PdAu alloys with compositions in supercells of X=14.18%, 25.93%, 37.07%, and 48.15% with the nearest (NNs) and next nearest neighbors (NNNs) varied over the entire range of compositions. The estimates were then used to obtain a model relating the O, T, and TS energies of a given site with NNX, NNNX, and the lattice constant.

Theoretically predicted rate constants for mercury oxidation by hydrogen chloride in coal combustion flue gases

In this work, theoretical rate constants are estimated for mercury oxidation reactions by hydrogen chloride that may occur in the flue gases of coal combustion. Rate constants are calculated using transition state theory at the quadratic configuration interaction (QCI) level of theory with single and double excitations, and are compared to results obtained from density functional theory, both including high level pseudopotentials for mercury. Thermodynamic and kinetic data from the literature are used to assess the accuracy of the theoretical calculations when possible. Validation of the chosen methods and basis sets is based upon previous and current research on mercury reactions involving chlorine. The present research shows that the QCISD method with the 1992 Stevens et al. basis set leads to the most accurate kinetic and thermodynamic results for the oxidation of mercury via chlorine containing molecules.