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Ammonia, primarily made with Haber-Bosch process developed in 1909 and winning two Nobel prizes, is a promising noncarbon fuel for preventing global warming of 1.5 °C above pre-industrial levels. However, the undesired characteristics of the process, including high carbon footprint, necessitate alternative ammonia synthesis methods, and among them is chemical looping ammonia production (CLAP) that uses nitrogen carrier materials and operates at atmospheric pressure with high product selectivity and energy efficiency. To date, neither a systematic review nor a perspective in nitrogen carriers and CLAP has been reported in the critical area. Thus, this work not only assesses the previous results of CLAP but also provides perspectives towards the future of CLAP. It classifies, characterizes, and holistically analyzes the fundamentally different CLAP pathways and discusses the ways of further improving the CLAP performance with the assistance of plasma technology and artificial intelligence (AI).

CO2 reduction under simulated sunlight over photocatalysts has become an attractive researcher area recently. In this work, carbon nitride compounds modified by TiO2 nanoparticles (TNPs) have been used for the photoreduction of CO2 in the presence of CH4 at room temperature. Briefly, a series of noble-metal-free TNP-graphitic-carbon nitride (g-C3N4, also abbreviated CN) photocatalysts with different TNPs loadings and calcination temperatures have been synthesized by a wet-chemical method. The characterization results of XRD, FTIR, SEM, TEM, BET, XPS, CO2 Adsorption, UV-vis, and PL demonstrate that the BET surface area and CO2 adsorption capacity have been improved after the calcination. Besides, the g-C3N4 has been successfully coupled with the TNPs and a heterojunction has formed at their interface. These characters contribute to increase the photocatalytic activity of TNPs-CN toward reducing CO2 in the presence of CH4, and its’ performance is better than bare g-C3N4, Titania (P25)-CN, MgO-CN, or Cu2O-CN. Orthogonal experiments are then carried out to investigate the sensitivity factors and optimum conditions. The sensitivity results show that the reaction pressure makes little difference on the photocatalysis results, which verifies the photoinduced CO2-CH4 reaction has a tiny change in gas volume. In addition, under the optimum conditions, the turnover frequency (TOF) of CO after 4 h reaction can reach 9.98 μmol g-cat.−1 h−1, and traces of ethane and ethylene have been detected during the reactions. In addition, surface acetate and carbonaceous deposit are found on the (20)TNPs-CN/450 surface after continuous 24 h irradiation under the optimum conditions, which resulting in the inactivation of the catalyst. Finally, possible reaction mechanisms have been proposed based on the results.

We demonstrate the development of a new atmospheric pressure-atomic layer deposition(AP-ALD) system to coat the inner walls of capillary columns for gas chromatography (GC). Unlike traditional ALD, this reactor operates at near-atmospheric pressure and addresses the challenges of depositing thin films inside capillaries, which include long pump down times, deposition in high-aspect-ratio materials, and temperature control. We show ALD of alumina in 5 and 12 m capillaries (0.53 mm ID) via sequential half reactions of trimethylaluminum and water. Our system yields pinhole-free, uniform thin films. It includes small witness chambers for witness silicon shards before and after the capillary. An engineering flow/transport analysis of the device is provided. Our ALD alumina thin films are characterized by spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy. Alumina film growth achieved is 1.4-1.5 Å/cycle, which is consistent with previously reported results. Film thickness measurements by SE on witness shards of silicon and by TEM at both ends of the capillary are in good agreement. A capillary column coated with alumina is used to separate different gases by GC, although the retention times of gases are essentially the same as with an untreated fused silica capillary. This successful deposition of ALD alumina in long capillaries opens the door for other possible ALD coatings, including hybrid organic-inorganic coatings, using the 450+ ALD precursors available today.

Direct conversion of greenhouse gas carbon dioxide (CO2) into lower olefins (ethylene, propylene and butene) provides an appealing approach to tackle CO2 emission challenges. Admixed catalysts composed of metal/metal oxides and SAPO-34 have been widely used for catalytic CO2 hydrogenation to lower olefins. However, interactions between metal/metal oxides and SAPO-34 remain obscure. Here, a novel family of admixed catalysts composed of Fe–Cu–K and SAPO-34 (Fe–Cu–K/SAPO) is developed for efficient catalytic CO2 hydrogenation to lower olefins, which can achieve 49.7% CO2 conversion and 62.9% selectivity of lower olefins, with CO selectivity

The aim of the present work is to provide a preliminary support and research foundation for developing integrated technology of methane dry reforming and pine wood pyrolysis to produce high value chemicals and fuels. The chemical properties of bio-oil produced by pine wood pyrolysis under traditional N2, H2, CO2, CH4 atmospheres and mixtures of CH4 and CO2 were investigated. Experimental studies were conducted in a fixed bed reactor at a temperature of 500 °C. The results show that pine wood pyrolysis under mixtures of methane and CO2 can promote bio-oil production (0.98% increase) compared with traditional pyrolysis (under N2). GC-MS results show that the contents of phenols and sugars in bio-oil decreased, while the amount of alcohols, aldehydes, ketones, and furans increased. NMR spectroscopy provides additional support of the results. Results indicate that bio-oil can be used as a source of value-added chemicals. High proportions of CO were obtained in the gas products from pine wood pyrolysis under CH4 and mixtures of CH4 and CO2. Finally, a possible reaction pathway of pine wood pyrolysis under mixtures of methane and CO2 is proposed. Methane bi-reforming with CO2 and steam from pine wood pyrolysis could promote the production of high value oxygen-containing chemicals during pine wood pyrolysis under mixtures of CH4 and CO2.

Direct synthesis of dimethyl ether (DME) by CO2 hydrogenation has been investigated over three hybrid catalysts prepared by different methods: co-precipitation, sol-gel, and solid grinding to produce mixed Cu, ZnO, ZrO2 catalysts that were physically mixed with a commercial ferrierite (FER) zeolite. The catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption of CO2 (CO2-TPD), temperature programmed desorption of NH3 (NH3-TPD), and temperature programmed H2 reduction (H2-TPR). The results demonstrate that smaller CuO and Cu crystallite sizes resulting in better dispersion of the active phases, higher surface area, and lower reduction temperature are all favorable for catalytic activity. The reaction mechanism has been studied using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Methanol appears to be formed via the bidentate-formate (b-HCOO) species undergoing stepwise hydrogenation, while DME formation occurs from methanol dehydration and reaction of two surface methoxy groups.

This comprehensive critical review combines, for the first time, recent advances in nanoscale surface chemistry, surface science, DFT, adsorption calorimetry, and in situ XRD and TEM to provide new insights into catalyst sintering. This work provides qualitative and quantitative estimates of the extent and rate of sintering as functions of nanocrystal (NC) size, temperature, and atmosphere. This review is unique in that besides summarizing important, useful data from previous studies, it also advances the field through addition of (i) improved or new models, (ii) new data summarized in original tables and figures, and (iii) new fundamental perspectives into sintering of supported metals and particularly of chemical sintering of supported Co during Fischer-Tropsch synthesis. We demonstrate how the two widely accepted sintering mechanisms are largely sequential with some overlap and highly NC-size dependent, i.e., generally, small NCs sinter rapidly by Ostwald ripening, while larger NCs sinter slowly by crystallite migration and coalescence. In addition, we demonstrate how accumulated knowledge, principles, and recent advances, discussed in this review, can be utilized in the design of supported metal NCs highly resistant to sintering. Recommendations for improving the design of sintering experiments and for new research are addressed.

Developing highly reactive, durable and low-cost oxygen carrier (OC) is the key to the advancement of the chemical looping combustion (CLC) technology that is regarded as the most energy-efficient way for the capture of CO2 emitted from fossil fuel combustion. In this study, the byproduct from coal power plant, coal fly ash (FA) was utilized as the support for Cu-based OC in methane CLC. Its performance was investigated with a thermogravimetric analyzer and a lab-scale fixed bed reactor. The results showed the FA is better as a support of OC than the most commonly used Al2O3 in anti-carbon deposition and thus beneficial to the importance of the stability of FA supported OCs. Among all the tested OCs, the Cu-based OC synthesized with FA support and impregnation method demonstrated the best performance, with CH4 conversion of 94–100% and CO2 selectivity of 91–94% in ten cycles at 800–850 °C, and minor deactivation. The characterization of the fresh and spent OCs revealed that the FA support itself could provide 1.0–2.9 wt% active oxygen for fuel combustion, which is enabled by the iron oxide in FA. In addition, the distribution of Cu on the FA support became more uniform on spent OC than on the fresh one. Also, the partially irreversible CuO decomposition into Cu2O during cyclic tests was the main reason for the deactivation of OC. Thus, Use of FA as an OC support is conducive to both development of cost-effective CLC and an environmental-friendly utilization of waste FA.

Oxy-fuel combustion has received significant attention because it is widely considered to be a promising method for cost-effective CO2 capture. The key to the success of oxy-fuel combustion processes is the availability of inexpensive O2. Therefore, development of low-cost and robust technologies for air separation or separating O2 from air is critical. Great progress has been made in this research and development area. However, a recent review of the progress made in the area is lacking. This review is designed to fill the gap. The review focuses on three major technologies for separating oxygen from air, including membranes, adsorption, and chemical-looping with oxygen uncoupling. The separation principles, characteristics, challenges and the associated solutions of these major technologies are systematically discussed. Future opportunities are outlined for each.

A series of silver-promoted, 20 wt% cobalt Fischer-Tropsch synthesis (FTS) catalysts supported on an alumina modified with 5 wt% silica were prepared using two methods: traditional incipient wetness impregnation (IWI) and a new solvent deficient precipitation (SDP) technique. Catalysts containing silver promoter concentrations of 0.3, 0.6, 1.2, and 2.5 wt% were prepared using each of the two methods. Silver improved the reducibility of the cobalt significantly, lowering reduction temperatures by up to 100 °C, and increasing the extent of reduction by up to 35%. Further, in both preparation methods, changing the silver loading altered the cobalt dispersion. The smallest Co crystallite size was achieved with 1.2 wt% Ag loading, which produced average cobalt crystallite sizes of about 7 nm. The Fischer-Tropsch CO consumption rate increased with decreasing crystallite size and thus was highest for 1.2 wt% Ag. Intrinsic CO consumption rates per Co site (CO turnover frequency) were also measured for each catalyst. A clear increase in the intrinsic turnover frequency (TOF) was observed as Ag loading was increased from 0.6% to 1.2 wt% for both preparation methods. Both 1.2 wt% Ag catalysts produced TOF’s of ∼0.050 s −1 (equivalent to a CO consumption rate of ∼65 mmol g cat −1 h −1 ), which are 20–30% higher than the catalysts containing 0.3, 0.6, and 2.5 wt% Ag and are comparable to reported rates for commercial FTS catalysts. Higher loadings of Ag (2.5 wt%) resulted in higher extents of reduction, but led to lower TOFs and larger Co crystallite diameters, which is assumed to be due to blockage of active sites and changes in the Ag-Ag and Ag-Co coordination ratio. Thus, silver promotion appears to improve catalytic performance by enhancing cobalt reduction, dispersion, and electronic properties. The SDP and IWI methods produced catalysts with essentially the same properties, but the SDP method is a simpler, one-pot technique that offers many potential advantages.

Low temperature oxidative dehydrogenation catalysts are becoming a viable material for drastically altering the production of small chain alkenes. Among materials used, bimetallic and trimetallic nickel catalysts have shown great promise. In this study, we report a 38% increase in the rate of ethylene production with the addition of Ce to NiNb catalysts. Oxidative dehydrogenation of ethane was performed in the temperature range of 250–350 °C. At 300 °C, the rate of ethylene production was maximized with a rate of 6.91 × 10–4 mmol gcat–1 s–1. At higher temperatures, the rate of deep oxidation to CO2 outcompeted the rate of ethylene formation. The improved rate due to the addition of Ce is attributed to ceria’s ability to rapidly transport oxygen to the NiO active sites.

Four identically-prepared 20 wt% cobalt/0.15 wt% ruthenium Fischer-Tropsch catalysts, supported on different aluminas, were synthesized by incipient wetness impregnation, characterized, and compared based on their performance under standard Fischer-Tropsch synthesis conditions. Three alumina supports were obtained from commercial sources (Sasol, St. Gobain, and Alfa Aesar), while the fourth was made using a published technique that included 5 wt% silica. The silica-stabilized alumina catalyst produced superior Fischer-Tropsch rates of 49 mmol CO/gcat h, compared to the other catalysts on the commercial supports with rates of 26–39 mmol CO/gcat h. The improved performance of the silica-stabilized alumina support compared to the commercially available aluminas is ascribed to a bimodal pore structure with larger average diameters and enhanced thermal stability. The support can be thermally treated to higher temperatures (e.g., 1100 °C) without transformation into α-alumina, allowing dehydroxylation of the surface prior to impregnation to stabilize a nearly ideal dispersion of cobalt crystallites.

CO 2 capture and utilization caused more and more public attention because of its environmental impact. The objective of this work was to study the catalytic gasification of a sub-bituminous coal from the Powder River Basin (PRB) using a CO 2 and H 2 O mixture as the gasifying agent. Sodium and iron, in the form of inexpensive compounds, were chosen to catalyze the coal gasification. The experiments were conducted between 700 and 900 °C in a fixed-bed laboratory gasifier under the atmospheric pressure. Results show that the added catalysts had an effect on the composition of gas products in a way different from it in pure steam gasification. Fitting models for kinetic data were examined and the results show that addition of 3 wt% Na or 3 wt% iron led to a 28.0% or a 19.5% reduction in the activation energy of the gasification reaction, respectively. The sodium and iron in the coal char were characterized and the results show that sodium is more evenly distributed than iron during gasification. Suggestions for improving the catalysts' performance in coal gasification were proposed accordingly.

Recently, carbon dioxide capture and conversion, along with hydrogen from renewable resources, provide an alternative approach to synthesis of useful fuels and chemicals. People are increasingly interested in developing innovative carbon dioxide hydrogenation catalysts, and the pace of progress in this area is accelerating. Accordingly, this perspective presents current state of the art and outlook in synthesis of light olefins, dimethyl ether, liquid fuels, and alcohols through two leading hydrogenation mechanisms: methanol reaction and Fischer-Tropsch based carbon dioxide hydrogenation. The future research directions for developing new heterogeneous catalysts with transformational technologies, including 3D printing and artificial intelligence, are provided., Carbon dioxide (CO2) capture and conversion provide an alternative approach to synthesis of useful fuels and chemicals. Here, Ye et al. give a comprehensive perspective on the current state of the art and outlook of CO2 catalytic hydrogenation to the synthesis of light olefins, dimethyl ether, liquid fuels, and alcohols.

A novel solvent deficient precipitation (SDP) method to produce nanoparticles was studied for its potential in Fischer-Tropsch synthesis (FTS) catalysis. Using Fe(NO3)3·9H2O as the iron-containing precursor, this method produces ferrihydrite particles which are then dried, calcined, reduced, and carbidized to form the active catalytic phase for FTS. Six different drying profiles, including final drying temperatures ranging between 80 and 150°C, were used to investigate the effect of ammonium nitrate (AN), a major by-product of reaction between Fe(NO3)3·9H2O and NH4HCO3 in the SDP method. Since AN has two phase-transitions within this range of drying temperatures, three different AN phases can exist during the drying of the catalyst precursors. These AN phases, along with physical changes occurring during the phase transitions, may affect the pore structure and the agglomeration of ferrihydrite crystallites, suggesting possible reasons for the observed differences in catalytic performance. Catalysts dried at 130°C showed the highest FTS rate and the lowest methane selectivity. In general, better catalytic performance is related to the AN phase present during drying as follows: phase III > phase II > phase I. However, within each AN phase, lower drying temperatures led to better catalytic properties.

The kinetics of a supported iron Fischer–Tropsch (FT) catalysts were investigated and a physically meaningful model that fits the data very well is proposed. Kinetic data (reported herein) were obtained at 250 °C and 20 atm in a fixed bed reactor at a variety of P H 2 and P CO. Measured P H 2 and P CO power law dependencies were found to be in the same range as those for unsupported Fe FT catalysts previously reported. The kinetic models in this study were tested using a statistical lack-of-fit test. Eight, two-parameter Langmuir–Hinshelwood rate expressions based on various mechanistic routes and assumptions were derived and tested, but all gave relatively poor fits to the data. An adjustment of the P H 2 dependency of the derived expressions to the 0.875 power resulted in three reasonable semi-empirical models, one of which fit the data extremely well. This approach also allowed us to determine the best function of P CO dependency. The results suggest that supported Fe FT catalysts follow a direct CO dissociation pathway, that carbon is one of the most abundant species on the surface of the catalyst, and that the hydrogenation of either C* or CH* is the rate-determining step.

This research is designed to make progress in overcoming the challenges through the development of a two-stage coal processing. Specifically, a two-stage process was used to maximize the use of the carbon in coal or increase the carbon monoxide yield or lower carbon dioxide and methane yields. Carbon dioxide-char gasification in the absence of water can generate carbon monoxide with near-zero methane, which is desired to produce high-carbon and low-hydrogen chemicals such as oxalic acid through catalytic carbon monoxide coupling and hydrolysis. The technology is applicable to any coal, although Power River Basin (PRB) coal is used as an example feedstock in this research Also, the sodium-iron catalyst can accelerate not only the reaction kinetics in both stages but also increase the hydrogen/carbon monoxide ratio in the syngas produced in the second stage. In other words, the catalyst is a multifunctional agent, which can not only intensify the overall coal process efficiency but also improve the qualities of the desired syngas products and reduce carbon dioxide emission. Thus, In the 1st stage, the catalysts can significantly reduce the CO2-char gasification by as high as 75.00%. In the 2nd stage, the H2/CO ratio of ideal syngas is ∼2:1 with near-0 CH4 generation and the CH4 production can be reduced as high as 61.29% for the CO2–H2O-Char coal gasification. The activation energy for the 2nd stage is reduced by as high as 35.43% than that of raw coal without use Na–Fe catalyst. The overall carbon footprint reduction for the study is reduced by 87.33% in the 1st stage and 96.77% compared to the direct coal combustion.

Coal is a rich-in-C and poor-in-H material. How should we maximize uses of C and H in coal for producing desired gases eventually converted to liquid chemicals with minimal CO2 emission? This research is designed to make progress in overcoming the challenges through development of a two-stage coal processing. The technology is applicable to any coal, although Power River Basin (PRB) coal is used as an example feedstock in this research. In the 1st stage or pyrolysis process of the low-carbon-footprint technology, a Na-Fe bimetallic catalyst was found to be able to not only enhance the yield of CO and ratio of H2/CO but also lower CH4 and CO2 yields with the presences of the Na-Fe catalyst, which are desired because the produced gas is an ideal syngas. In the 2nd stage or gasification of the char obtained from pyrolysis stage with CO2 for producing almost 100%-purity CO without presence of H2O. The CO2 as the major byproduct of the 1st stage could be used as a raw material in the 2nd stage, which is an ideal process integration for significant reduction in CO2 emission. Also, the Na-Fe catalyst can accelerate not only the reaction kinetics in both stages but also increase the H¬2/CO ratio in the syngas produced in the 2nd stage. In other words, the catalyst is a multifunctional agent, which can not only intensify the overall coal process efficiency but also improve the qualities of the products and reduce CO2 emission.

The production of ethylene via the oxidative dehydrogenation of ethane is well-documented as an energy efficient process. Alumina-supported NiO catalysts make the oxidative dehydrogenation of ethane more selective to ethylene and operate at low reaction temperatures ( × 10−2 μmolethylene/s·m2 at 500 °C.

This editorial is written to recognize Professor Emeritus Calvin H. Bartholomew, who celebrated his 75th birthday in 2018, and to introduce the commemorative issue of Catalysts compiled in his honor. Following a brief biography that celebrates the career and contributions of Professor Bartholomew, the nine articles that make up the special issue are briefly reviewed. Dr. Bartholomew is an eminent researcher, an outstanding educator, mentor, and friend.

The extent of reduction of unsupported iron-based high-temperature water-gas shift catalysts with small (

Catalyst deactivation, the loss over time of catalytic activity and/or selectivity, is a problem of great and continuing concern in the practice of industrial catalytic processes. Costs to industry for catalyst replacement and process shutdown total tens of billions of dollars per year. [...]

CO2 gasification of a sub-bituminous Wyodak coal from the Powder River Basin (PRB) was conducted in a fixed-bed laboratory gasifier at atmospheric pressure with FeCO3 as a catalyst precursor. The effect of iron on the coal pyrolysis was evaluated by thermo-gravimetric analysis (TGA). Scanning electron microscopy (SEM) was employed to characterize the iron performance in the char gasification. The iron species and oxidation states during the coal gasification, characterized by X-ray diffraction (XRD) and Mossbauer spectroscopy, indicate a complex interaction between the reaction atmosphere and temperature, but generally proceed through reduction to FeO and metallic iron during pyrolysis, followed by subsequent reoxidation to Fe3O4 during gasification with CO2. The catalytic effect of iron was also quantitatively evaluated by kinetic analysis using shrinking core and random pore models, with the shrinking core model providing superior results. Results show that the apparent activation energy was 92.7 kJ/mol for the untreated coal, which decreased to 58.3 kJ/mol for the coal with 3 wt% Fe. FeCO3 was shown to have a significant catalytic effect on the Wyodak coal gasification with CO2.

Transfer limitations were successfully modeled and optimized for iron-based catalysts for Fischer–Tropsch synthesis. The simulation model predicts the effect of changing reaction temperatures, reaction pressures, catalyst pellet size, and the feed CO composition on pore diffusion, film heat transfer, internal heat transfer, and pressure drop. The comprehensive contour maps obtained from the model quantitatively display the effects of these various design variables to both optimize catalyst design and provide guidance for kinetic experiments. The optimization results favor higher reaction temperatures and pressures, smaller pellet sizes, and lower feed CO compositions to maintain high activity of kinetically-controlled reaction rates. The optimal temperature (255.8 °C) was constrained by the rate of catalytic deactivation. The model was validated by experimental data acquired from a fixed-bed reactor and shows excellent agreement. The model predicts the observed rate to be 79% of the intrinsic rate at 250 °C, 20 bar, equimolar H2:CO, and 425 μm pellet size, while experimental results showed this percentage was 74 ± 7% for 250–600 μm pellets. The model predicts no pore-diffusion limitations at pellet sizes smaller than 250 μm, indicating that the reaction rate is kinetically-controlled. Furthermore, the resistance due to film temperature gradients is more limiting than that due to intraparticle temperature gradients. Finally, pressure drop was well below 10% of the inlet reactor pressure under laboratory-scale conditions. The model was used to predict the effect of using smaller catalyst pellets on pressure drop for a commercial-scale reactor, which showed that acceptable operation could be expected with a pressure drop of 20% of the inlet reactor pressure.

Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with reference to the latest literature reports in these areas. Two case studies on the deactivation mechanisms of catalysts used for cobalt Fischer-Tropsch and selective catalytic reduction are considered to provide additional depth in the topics of sintering, coking, poisoning, and fouling. Regeneration considerations and options are also briefly discussed for each deactivation mechanism.

The effects of Co on RuO 2 /Al 2 O 3 's activities for water gas shift (WGS) and methanation were studied. Catalysts were characterized with BET, XRD, SEM/EDS, H 2 -TPR and CO-TPR. The effects of various parameters, such as calcination temperature, Ru–Co loading, Ru/Co ratio, inlet CO concentration and H 2 O/CO ratio on the activities of catalysts were investigated. There existed Co I (strongly interact with RuO 2 ) and Co II (weakly interact with RuO 2 ). For Co/RuO 2 /Al 2 O 3 (Ru/Co = 1, AT = 350), only Co I existed as bimetallic Co–Ru nanoparticles. This unique structure led this catalyst to achieve the highest CO conversion of 98.6% exceeding WGS's theoretical thermodynamic equilibrium limit due to the co-occurrence of methanation. Co/RuO 2 /Al 2 O 3 was more favorable to catalyze CO methanation than CO 2 methanation. The apparent activation energies of forward and reverse WGS catalyzed by Co/RuO 2 /Al 2 O 3 were 37.8 and 74.6 kJ mol −1 , respectively. The difference was corresponding well to the enthalpy change (−41.1 kJ mol −1 ) of WGS.

The objective of this work is to comprehensively investigate the pyrolysis characteristics of the direct coal liquefaction residue (DCLR) from China Shenhua industrial direct coal liquefaction plant. The pyrolysis experiments were conducted with TGA under four kinds of atmospheres (N2, 10% H2, CO2, and air) and a fixed bed reactor in N2. Two obvious mass loss peaks at 470 °C and 770 °C, are mainly attributed to decomposition of the organic matrix and inorganic compounds in DCLR, respectively. The four fractions extracted from DCLR (hexane soluble fraction (HS), asphaltene fraction (A), preasphaltene (PA), and tetrahydrofuran insoluble (THFIS)) were studied separately by TG-FTIR, and the results show that the interaction among the fractions is unfavorable for the evolution of volatile matter. In addition, the inorganic compounds in DCLR exhibit catalysis behaviors on both pyrolysis under N2 and gasification under CO2. Moreover, the properties of DCLR pyrolysis products obtained from the fixed bed reactor were analyzed by GC–MS, SEM, and FTIR. Finally, a kinetic analysis of DCLR pyrolysis was performed using the distributed activation energy model (DAEM). The activation energy distribution of DCLR follows an approximate Gaussian distribution with a mean activation energy of 87.6 kJ/mol.

The structural and functional roles of varying amounts of lanthana in co-precipitated high temperature Fe2O3/Cr2O3/CuO water–gas shift catalysts were studied at 1 atm and 350–425 °C temperature range. Addition of 0.5 wt% of lanthana enhanced the reducibility of the catalyst, increased its surface area and its WGS activity from 24 to 31 mmol CO/(gcat min), and reduced the deactivation rate at 400 °C from 23% to 11% relative to a similar catalyst with no lanthana. XRD results suggested that 0.5 wt% of lanthana stabilized the iron–chromium cubic spinel structure most efficiently under the operating conditions; however, further additions appeared to disrupt the spinel structure and degrade the performance of the catalysts. The power-law and Langmuir–Hinshelwood models provided much better fits to the rate data than either the redox or the Eley–Rideal models, suggesting that the reaction tends to follow an adsorptive mechanism. The CO adsorption equilibrium constant was largest for the catalyst with 0.5 wt% lanthana, indicating that the addition of lanthana might facilitate CO adsorption. Water inhibited the reaction as it strongly adsorbed on the catalyst surface.

Globally, coal-fired power plants are the largest industrial source of carbon dioxide (CO2). CO2 emissions from flue gas have potential for direct mineralization with electrostatic precipitator fly ash particles in the field. Demonstration scale accelerated mineral carbonation (AMC) studies were conducted at the Jim Bridger Power Plant, a large coal fired power plant located in Wyoming, USA. AMC produces kinetically rapid conditions for increased rates of mineralization of CO2, sulfur dioxide (SO2) and mercury (Hg) on fly ash particles. Control and AMC reacted fly ash particles were investigated for: change in carbon (expressed as CaCO3), sulfur (expressed as SO42−), and mercury (Hg) contents; topology and surface chemical composition by scanning electron microscope/energy dispersive X-ray spectroscopy analysis; chemical distribution of trace elements; and aqueous mineral solubility by the toxicity characteristic leaching procedure. Results of the AMC process show an increase in C, S, and Hg on AMC fly ash particles suggesting that multiple pollutants from flue gas can be removed through this direct mineral carbonation process. Results also suggest that the AMC process shifts soluble trace elements in fly ash to less leachable mineral fractions. The results of this study can provide insight into potential successful field implementation of AMC.

The objective of this study is to compare the performance of several activated carbon (AC) based catalysts for CH 4 reforming with CO 2 , including raw AC and AC modified with HNO 3 and NaNO 3 , designated as AC-HNO 3 and AC-NaNO 3 , respectively. CH 4 –CO 2 reforming experiments were conducted in a fixed-bed reactor at temperatures from 700 °C to 1000 °C. The catalysts were characterized by various techniques, including Fourier Transform Infrared Spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) analysis, CO 2 chemisorption, temperature programmed oxidation–CO 2 (TPO–CO 2 ), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDX). The catalytic activities of the three catalysts are considerably different at low temperature, although they are similar at high temperature. At 700 °C, the average conversions of CH 4 and CO 2 over AC-NaNO 3 are 17.7% and 29.7%, respectively, which are 2.4 and 3.2 times higher than those over AC. At 1000 °C, the conversions of CH 4 and CO 2 exceed 90% over these three catalysts. In addition, the mole ratio of H 2 /CO increases with temperature for all the catalysts. The mole ratio of H 2 /CO over AC-HNO 3 , which is from 0.76 to 0.94 at different temperatures, is closer to 1 than that over the other two catalysts. Based on the characterization results, NaNO 3 is more instrumental to the formation of mesopores, surface oxygenated groups, and the reduction of deposited carbon. Hydroxyl group plays an important role in CH 4 –CO 2 reforming. According to TPO–CO 2 observations, two types of deposited carbon are formed during reforming reaction. The apparent activation energies of the CH 4 –CO 2 reforming reactions catalyzed by AC, AC-HNO 3 , and AC-NaNO 3 are 202 kJ/mol, 227 kJ/mol, and 123 kJ/mol.

The objective of this research is to study the effect of the composite catalyst, FeCO3–Na2CO3, on gasification of a low-sulfur sub-bituminous Wyodak coal from the Powder River Basin (PRB) of Wyoming. The catalytic effects of the composite catalysts were evaluated by comparing their effluent gas compositions and carbon conversion kinetics to those achieved in the presence of either FeCO3 or Na2CO3 catalyst alone or without the presence of any catalyst. All of the evaluation work was conducted in a fixed bed gasifier at atmospheric pressure. Compared to raw coal with no catalyst, the composite catalyst is efficient in increasing the carbon conversion rate constant by as much as two times within the 700–800 °C range due to its ability to reduce the activation energy of gasification by about 30–40%. Compared to pure sodium and iron catalysts, the composite catalyst can increase the yields of desired products H2 and CO at 800 °C by 15% and 40%, respectively. The composite catalyst can not only synergize the advantages, but also overcome the challenges of pure iron or pure sodium based catalytic coal gasification processes.

This paper investigates the effects of various, carefully-chosen preparation methods on the performance of Fischer–Tropsch (FT) alumina-supported iron/copper/potassium (FeCuK/Al2O3) catalysts. Two tested preparation methods (co-impregnation and non-aqueous slurry impregnation) yielded supported Fe catalysts with better catalyst performance than previously thought possible. These two supported iron catalysts have high reaction rates (114–154 mmol (CO + H2) gcat−1 MPa−1 h−1), good productivity (0.26–0.29 gHC gcat−1 h−1), and reasonable stability. In fact, both catalysts are more active than any supported Fe catalyst reported outside our group and compare favorably with unsupported catalysts. Superior activity, coupled with the high strength of a supported catalyst, make these catalysts excellent candidates for use in slurry bubble column reactor (SBCR) applications.

Catalytic gasification of a Wyodak low-sulfur sub-bituminous coal from the Powder River Basin of Wyoming was investigated using an inexpensive catalyst, Na 2 CO 3 , widely available in Wyoming. Experiments were performed in an atmospheric pressure fixed-bed laboratory gasifier. The effects of different factors including feed gas composition, catalyst loading and reaction temperature on the associated coal pyrolysis and char gasification were evaluated. Na 2 CO 3 was found to be active during both pyrolysis and gasification steps and it can considerably decrease the activation energy of gasification step. The optimal Na 2 CO 3 addition level is approximately 3 wt.%. Shrinking core model and random pore model can be used to fit the kinetic data obtained under both non-catalytic and catalytic conditions.

In this study, the adsorption performance of elemental mercury onto commercially produced Thief carbons (TCs) and TCs modi- fied with ferric chloride and sodium chloride were investigated. The results indicate that the modifications of Thief carbons not only con- siderably enhanced their mercury sorption capacities but also change their mercury sorption mechanism. For example, modification of a Thief carbon with ferric chloride can increase its mercury sorption capacity from 21 μg=g to 206 μg=g (nearly a ten times increase), whereas reducing its surface area from 326 m 2 =g to 217 m 2 =g. Ferric chloride is a better modification agent than sodium chloride. Analyses of the sorption mechanism with different tools, including X-ray photoelectron spectroscopy (XPS), indicate that physical sorption dominates raw Thief-carbons-based mercury sorption, whereas chemical sorption plays a much more important role in modified Thief-carbon-based mercury sorption. The reaction order and activation energy of ferric chloride modified Thief-carbon-based mercury chemisorption are 1 and 85: 6k J=mol·K, respectively. DOI: 10.1061/(ASCE)EE.1943-7870.0000434. © 2012 American Society of Civil Engineers.

An alternative method for using monoethanolamine (MEA) in CO2 separation is developed from the viewpoints of the MEA–CO2 reaction environment and the process of spent sorbent regeneration. MEA–TiO2 (MT) CO2 sorbent is synthesized using pure MEA and a support material, TiO2. The performance of the MT sorbent on CO2 separation was investigated in tubular reactors under various experimental conditions. The sorption capacity of the MT sorbent reached 1.09 mol-CO2/kg-MT at 45 wt % MEA. However, an optimum of 40 wt % MEA loading was chosen for most of the sorption tests. Temperature affected the CO2 sorption capacity considerably, with optimum values of 45 °C for adsorption and 90 °C for regeneration, while humidity had a small positive effect. TiO(OH)2 appears to be the best support material for MEA, but more evaluation is needed. The MT sorbent is regenerable, with a multicycle sorption capacity of ∼0.91 mol-CO2/kg-MT under the given experimental conditions.

Monoethanolamine (MEA)/macroporous TiO2 sorbent is a promising material for CO2 separation because of its low energy demand. Similar to other CO2 separation technologies, CO2 desorption from the MEA/macroporous TiO2 sorbent is the most energy-intensive step in the overall CO2 separation process. The presence of water during the CO2 desorption process leads to a significant increase in energy consumption. Therefore, CO2 desorption in the absence of water is an important method to reduce energy consumption of CO2 separation using MEA/macroporous TiO2, which is determined by several major factors, including desorption kinetics. However, the study on CO2 desorption kinetics of supported MEA is lacking. This research was designed to make progress in this area. The CO2 desorption kinetic model of the MEA/macroporous TiO2 sorbent is experimentally derived with the data collected within the water-free desorption environment and theoretically proven by the pseudo-steady-state theory. The Avrami–Erofeyev mechanism ...

The mineral carbonation, a process of converting CO 2 into stable minerals (mineralization), has been studied extensively to capture and store CO 2 . However, most of the mineral carbonation studies have been largely investigated at lab scale. Preliminary and pilot scale studies for accelerated mineral carbonation (AMC) were conducted at one of the largest coal-fired power plants (2120 MW) in the USA by reacting flue gas with fly ash particles in a fluidized bed reactor. In the preliminary experiments, flue gas CO 2 and SO 2 concentrations decreased from 13.0 to 9.6% and from 107.8 to 15.1 ppmv, respectively during the first 2 min. of reaction. The flue gas treatment increased mercury (Hg) concentration in fly ash (0.1 to 0.22 mg/kg) suggesting that fly ash particles also mineralized flue gas Hg. From these results, we designed and developed pilot scale process skid consisting — a moisture reducing drum (MRD) ( 0.9 m Φ × 1.8 m ), a heater/humidifier ( 0.9 m Φ × 1.8 m ), and a fluidized bed reactor (FBR) ( 0.9 – 1.2 m Φ × 3.7 m ) to capture and mineralize flue gas CO 2 . Flue gas was withdrawn from the stack and was fed to the MRD at about 0.094 m 3 /s. The MRD and the heater/humidifier pretreat flue gas before it enters the FBR. The MRD captures droplets of water entrained in the flue gas to protect the blower placed between the MRD and the heater/humidifier. The heater/humidifier enables control of flue gas moisture and temperature. Approximately 100–300 kg of fresh fly ash was collected from the electrostatic precipitator through ash hopper and placed in the fluidized-bed reactor. The fly ash particles were fluidized by flow of flue gas through a distributor plate in the FBR. The pilot scale studies were conducted at a controlled pressure (115.1 kPa) by controlling the flue gas moisture content. The flue gas was continuously monitored to measure flue gas CO 2 , SO 2 and NO x concentrations by an industrial grade gas analyzer, while the fresh and spent fly ashes were analyzed for calcium carbonate (CaCO 3 ), sulfur (S), and mercury (Hg) content. The pilot scale study results suggest that an appreciable amount of flue gas CO 2 and significant amounts of SO 2 and Hg can be directly captured (without separation) and mineralized by the fly ash particles.

Alumina (Al 2 O 3 ) was added as a component of conventional iron oxide-based high temperature water gas shift (WGS) catalysts. The catalysts contained Fe–Al–Cr–Cu–O and were synthesized by coprecipitation. A series of catalysts were prepared with 5–50 wt% Al 2 O 3 , 8 wt% Cr 2 O 3 , 4 wt% CuO, and the balance Fe 2 O 3 . One catalyst was prepared in which the chromia was replaced by alumina. All of the catalysts were compared to a reference WGS catalyst (88 wt% FeO x , 8 wt% Cr 2 O 3 , and 4 wt% CuO) with no alumina. The catalysts were characterized using temperature programmed reduction (TPR), surface area analysis using nitrogen physisorption, and scanning electron microscopy (SEM) with compositional analysis. The catalysts were also tested kinetically under WGS conditions. Addition of 10–15 wt% alumina increased the catalyst activity and thermal stability, with approximately 15 wt% alumina addition being optimum, as this catalyst produced a reaction rate (normalized per mass) 74% higher than the reference catalyst. The effect of alumina addition was greater than the surface area increase alone, which suggests that alumina alters the activity of the iron oxide domains, likely through an increase in reducibility, as shown by the TPR results. This synergistic effect was only observed when both alumina and chromia were present. Alumina alone (as a replacement for chromia) was not as an effective stabilizer as chromia. Although both the alumina-containing catalyst (without chromia) and the reference with chromia had similar initial surface areas (∼160 m 2 /g), the alumina-containing catalyst retained only 74% as much surface area after reaction. Results from the catalysts with 50 wt% alumina suggest that the loss of catalytic activity is also due to the formation of aluminates.

A novel pulsed corona wire-in-tube reactor with quartz view-ports allowed visual observation of the effect of charge voltage and gas composition on the corona distribution. The H2S conversion and energy efficiency of H2S decomposition in this pulsed corona discharge reactor varied at constant power (100 W) due to the selected values of the electrical parameters of pulse forming capacitance (720–2880 pF), charge voltage (11–21 kV), and pulse frequency (157–961 Hz). Low pulse forming capacitance, low charge voltage, and high pulse frequency operation produces the highest energy efficiency for H2S conversion at constant power. H2S conversion is more efficient in Ar–N2 gas mixtures than in Ar or N2. These results can be explained by corona discharge observations, the electron attachment reactions of H2S at the streamer energies, and a proposed reaction mechanism of H2S dissociation in the Ar–N2 gas mixture. The energy consumption per molecule of converted H2S in an equimolar mixture of Ar and N2 (4.9 eV/H2S) is the lowest that has been reported for any plasma reactor operated at non-vacuum pressures. The results reveal the potential for energy efficient H2S decomposition in pulsed corona discharge reactors.

Hydrogen sulfide ( H 2 S ) dissociation into hydrogen and sulfur has been studied in a pulsed corona discharge reactor (PCDR). Due to the high dielectric strength of pure H 2 S ( ∼ 2.9 times higher than air), a nonthermal plasma could not be sustained in pure H 2 S at discharge voltages up to 30 kV with our reactor geometry. Therefore, H 2 S was diluted with another gas with lower dielectric strength to reduce the breakdown voltage. Breakdown voltages of H 2 S in four balance gases (Ar, He, N 2 , and H 2 ) have been measured at different H 2 S concentrations and pressures. Breakdown voltages are proportional to the partial pressure of H 2 S and the balance gas. With increasing H 2 S concentrations, H 2 S conversion initially increases, reaches a maximum, and then decreases. H 2 S conversion and the reaction energy efficiency depend on the balance gas and H 2 S inlet concentrations. H 2 S conversion in atomic balance gases, such as Ar and He, is more efficient than that in diatomic balance gases, such as N 2 and H 2 . These observations can be explained by proposed reaction mechanisms of H 2 S dissociation in different balance gases. The results show that nonthermal plasmas are effective for dissociating H 2 S into hydrogen and sulfur.

Author(s): Popa, T; Fan, M; Argyle, MD; Dyar, MD; Gao, Y; Tang, J; Speicher, EA; Kammen, DM

This work reports the effect of capacitance, cathode material, gas flow rate and specific energy input on methane conversion, energy efficiency and product selectivity in a co-axial cylinder pulsed corona discharge reactor. Ethane and acetylene appear to be formed from dimerization of CH3 radicals and CH radicals, respectively, while ethylene is formed mainly from the dehydrogenation of ethane. At a given power input, low capacitance with high pulse frequency results in higher methane conversion and energy efficiency than operation at high capacitance with low pulse frequency. Platinum coated stainless steel cathodes slightly enhance methane conversion relative to stainless steel cathodes, perhaps due to a weak catalytic effect. As specific energy input increases, energy efficiency for methane conversion goes through a minimum, while the selectivity of acetylene has a maximum value. Comparison of methane conversion for different types of plasma reactors shows that the pulsed corona discharge is a potential alternative method for low temperature methane conversion.