Catalytic carbon dioxide hydrogenation to methane: A review of recent studies

Recently, various efforts have been put forward on the development of technologies for the synthesis of methane from CO2 and H-2, since it can offer a solution for renewable H-2 storage and transportation. In parallel, this reaction is considered to be a critical step in reclaiming oxygen within a closed cycle. Over the years, extensive fundamental research works on CO2 methanation have been investigated and reported in the literatures. In this updated review, we present a comprehensive overview of recent publications during the last 3 years. Various aspects on this reaction system are described in detail, such as thermodynamic considerations, catalyst innovations, the influence of reaction conditions, overall catalytic performance, and reaction mechanism. Finally, the future development of CO2 methanation is discussed. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

Modeling of the effect of hydrogen injection on blast furnace operation and carbon dioxide emissions

The effect of hydrogen injection on blast furnace operation and carbon dioxide emissions was simulated using a 1D steady-state zonal model.The maximum hydrogen injection rate was evaluated on the basis of the simulation of the vertical temperature pattern in the blast furnace with a focus on the thermal reserve zone.The effects of blast temperature and oxygen enrichment were also examined to estimate coke replacement ratio,productivity,hydrogen utilization efficiency,and carbon dioxide emission reduction.For blast temperature of 1200℃,the maximum hydrogen injection rate was 19.0 and 28.3 kg of H_(2)/t of hot metal(HM)for oxygen enrichment of 2vol%and 12vol%,respectively.Results showed a coke replacement ratio of 3-4 kg of coke/kg of H_(2),direct CO_(2) emission reduction of 10.2%-17.8%,and increased productivity by up to 13.7%depending on oxygen enrichment level.Increasing blast temperature further reduced the direct CO_(2) emissions.Hydrogen utilization degree reached the maximum of 0.52-0.54 H_(2)O/(H_(2)O+H_(2)).The decarbonization potential of hydrogen injection was estimated in the range from 9.4 t of CO_(2)/t of H_(2) to 9.7 t of CO_(2)/t of H_(2).For economic feasibility,hydrogen injection requires revolutionary progress in terms of low-cost H_(2) generation unless the technological change is motivated by the carbon emission cost.Hydrogen injection may unfavorably affect the radial temperature pattern of the raceway,which could be addressed by adopting appropriate injection techniques.

Direct carbon dioxide hydrogenation to produce bulk chemicals and liquid fuels via heterogeneous catalysis

The hydrogenation of carbon dioxide(CO_(2))to produce chemicals and transportation liquid fuels in huge demand via heterogeneous thermochemical catalysis achieved using renewable energy has received increasing attention,and substantial advances have been made in this research field in recent years.In this study,we summarize our progress in the rational design and construction of highly efficient catalysts for CO_(2) hydrogenation to methanol,lower olefins,aromatics,and gasolineand jet fuel-range hydrocarbons.The structure‐performance relationship,nature of the active sites,and mechanism of the reactions occurring over these catalysts are explored by combining computational and experimental evidence.The results of this study will promote further fundamental studies and industrial applications of heterogeneous catalysts for CO_(2) hydrogenation to produce bulk chemicals and liquid fuels.

Catalytic hydrogenation performance of ZIF-8 carbide for electrochemical reduction of carbon dioxide

The conversion of CO_(2) electrocatalytic hydrogenation into energy-rich fuel is considered to be the most effective way to carbon recycle.Nitrogen-doping carbonized ZIF-8 is proposed as carrier of the earth-rich Sn catalyst to overcome the limit of electron transfer and CO_(2) adsorption capacity of Sn.Hierarchically porous structure of Sn doped carbonized ZIF-8 is controlled by hydrothermal and carbonization conditions,which induces much higher specific surface area than that of the commercial Sn nanoparticle(1003.174 vs.7.410 m^(2)·g^(-1)).The shift of nitrogen peaks in X-ray Photoelectron Spectroscopy spectra indicates interaction between ZIF-8 and Sn,which induces the shift of electron cloud from Sn to the chemical nitrogen to enhance conductivity and regulate electron transfer from catalyst to CO_(2).Lower mass transfer resistance and Warburg resistance are investigated through EIS,which significantly improves the catalytic activity for CO_(2) reduction reaction(CO_(2)RR).Onset potential of the reaction is reduced from-0.74 V to less than-0.54 V vs.RHE.The total Faraday efficiency of HCOOH and CO reaches 68.9%at-1.14 V vs.RHE,which is much higher than that of the commercial Sn(45.0%)and some other Sn-based catalyst reported in the literature.

Effects of zinc on χ-Fe_(5)C_(2) for carbon dioxide hydrogenation to olefins:Insights from experimental and density function theory calculations

Production of light olefins from CO_(2), the primary greenhouse gases, is of great importance to mitigate the adverse effects of CO_(2) emission on environment and to supply the value-added products from nonpetroleum resource. However, development of robust catalyst with controllable selectivity and stability remains a challenge. Herein, we report that Zn-promoted Fe catalyst can boost the stable and selective production of light olefins from CO_(2). Specifically, the Zn-promoted Fe exhibits a highly stable activity and olefin selectivity over 200 h time-on-stream compared to the unpromoted Fe catalyst, primarily owing to the preservation of active χ-Fe_(5)C_(2) phase. Structural characterizations of the spent catalysts suggest that Zn substantially regulates the content of iron carbide on the surface and suppresses the reoxidation of bulk iron carbide during the reaction. DFT calculations confirm that adsorption of surface carbon atoms and graphene-like carbonaceous species are not thermochemically favored on Zn-promoted Fe catalyst. Carbon deposition by CAC coupling reactions of two surface carbon atoms and dehydrogenation of CH intermediate are also inhibited. Furthermore, the effects of Zn on antioxidation of iron carbide were also investigated. Zn favored the hydrogenation of surface adsorbed oxygen atoms to H_(2)O and the desorption of H_(2)O, which reduces the possibility of surface carbide being oxidized by the chemisorbed oxygen.

Experimental Design Technique on Removal of Hydrogen Sulfide using CaO-eggshells Dispersed onto Palm Kernel Shell Activated Carbon：Experiment,Optimization,Equilibrium and Kinetic Studies

This study presents the use of chicken eggshells waste utilizing palm kernel shell based activated carbon（PKSAC） through the modification of their surface to enhance the adsorption capacity of H2S. Response surface methodology technique was used to optimize the process conditions and they were found to be： 500 mg/L for H2S initial concentration, 540 min for contact time and 1 g for adsorbent mass. The impacts of three arrangement factors（calcination temperature of impregnated activated carbon（IAC）, the calcium solution concentration and contact time of calcination） on the H2S removal efficiency and impregnated AC yield were investigated. Both responses IAC yield（IACY, %） and removal efficiency（RE, %） were maximized to optimize the IAC preparation conditions. The optimum preparation conditions for IACY and RE were found as follows： calcination temperature of IAC of 880 ℃, calcium solution concentration of 49.3% and calcination contact time of 57.6 min, which resulted in 35.8% of IACY and 98.2% RE. In addition, the equilibrium and kinetics of the process were investigated. The adsorbent was characterized using TGA, XRD, FTIR, SEM/EDX, and BET. The maximum monolayer adsorption capacity was found to be 543.47 mg/g. The results recommended that the composite of PKSAC and Ca O could be a useful material for H2S containing wastewater treatment.

Renewable Methanol Production Using Captured Carbon Dioxide and Hydrogen Generated through Water-Splitting

The global warming issues associated with fossil fuels have forced the world to shift towards environment-friendly alternatives. The studies on the capture and storage of CO2 have gained significant research attention, and to attract the world towards CO2 capturing and storing, it is necessary to find suitable applications for this captured CO2. Methanol is one of the products which can be produced by utilizing the captured CO2 and hydrogen that can be produced by water splitting. Keeping in view both these green fuel production processes, this study proposes a combined application of both these technologies for the production of methanol, which is an important chemical used in manufacturing industries. This review paper presents a brief study of both carbon capture and hydrogen production technologies. It also provides research trends, economic aspects, and methods of incorporating both these technologies to produce methanol. Additionally, the prospects of the approach in Oman have also been presented.

Organic Fuel Synthesis from Atmospheric Carbon Dioxide and Hydrogen Produced from Water by Electrolysis

Synthesis of organic fuels from carbon dioxide and hydrogen is analysed,in terms of energy recovery efficiency,and the required energy input for electrolysis of water.This electrical energy is related to the thermal energy required in a power station.A method is described to recover heat from energy-producing reactions in the fuel synthesis process,which can then be used to reduce the electrical energy requirement for electrolysis.By co-locating the fuel synthesis plant with a thermal power station,primary(thermal) energy can be used to produce high temperature steam,with a lower electrical requirement for electrolytic production of hydrogen.This can make more efficient use of the primary energy than a thermodynamic engine.Comparison is made with alternative fuels,in terms of energy budget,sustainability,carbon dioxide emissions,etc.The energy security benefits of advanced fuel synthesis are also identified.

Recent advances in carbon dioxide selective hydrogenation and biomass valorization via single-atom catalysts

The utilization of fossil fuels has brought unprecedented prosperity and development to human society,but also caused environmental pollution and global warming triggered by excess greenhouse gases emission.For one thing,the excess emission of carbon dioxide(CO_(2)),which has a negative impact on global temperature and ocean acidity,needs to be controlled.For another,the depletion of fossil fuels will eventually force people to seek alternative carbon sources to maintain a sustainable economy.Thus,using renewable energy to convert CO_(2) and biomass into value-added chemicals and fuels is a promising method to overcome urgent problems.The hy-drogenation of CO_(2) is very important to mitigate the greenhouse effect caused by CO_(2),while biomass conversion can produce alternative renewable biofuels and green chemicals.As a kind of promising catalyst,heterogeneous single-atom catalyst(SAC)has received extensive attention in the past decades.SACs combine the advantages of homogeneous catalysts with uniform active sites and heterogeneous catalysts that are easily separable.In this review,we will give a comprehensive overview of the latest progress in CO_(2) selective hydrogenation and biomass conversion via SACs.

Interfacial engineering of graphitic carbon nitride(g-C_3N_4)-based metal sulfide heterojunction photocatalysts for energy conversion: A review

As one of the most appealing and attractive technologies, photocatalysis is widely used as a promising method to circumvent the environmental and energy problems. Due to its chemical stability and unique physicochemical, graphitic carbon nitride (g-C3N4) has become research hotspots in the community. However, g-C3N4 photocatalyst still suffers from many problems, resulting in unsatisfactory photocatalytic activity such as low specific surface area, high charge recombination and insufficient visible light utilization. Since 2009, g-C3N4-based heterostructures have attracted the attention of scientists worldwide for their greatly enhanced photocatalytic performance. Overall, this review summarizes the recent advances of g-C3N4-based nanocomposites modified with transition metal sulfide (TMS), including (1) preparation of pristine g-C3N4,(2) modification strategies of g-C3N4,(3) design principles of TMS-modified g-C3N4 heterostructured photocatalysts, and (4) applications in energy conversion. What is more, the characteristics and transfer mechanisms of each classification of the metal sulfide heterojunction system will be critically reviewed, spanning from the following categories:(1) Type I heterojunction,(2) Type II heterojunction,(3) p-n heterojunction,(4) Schottky junction and (5) Z-scheme heterojunction. Apart from that, the application of g-C3N4-based heterostructured photocatalysts in H2 evolution, CO2 reduction, N2 fixation and pollutant degradation will also be systematically presented. Last but not least, this review will conclude with invigorating perspectives, limitations and prospects for further advancing g-C3N4-based heterostructured photocatalysts toward practical benefits for a sustainable future.

Oil-soluble Ni-Mo sulfide nanoparticles and their hydrogenation catalytic properties

Oil-soluble bimetallic Ni-Mo sulfide nanoparticles（NiMoS） with narrow size distribution were successfully synthesized through a composite-surfactants-assisted-solvothermal process.The surface functionality and lipophilicity of the Ni-Mo sulfides were shown by transmission electronic microscopy,Fourier transform infrared and ultraviolet spectroscopy.The as-prepared Ni-Mo sulfides supported on activated carbon（NiMoS/AC） exhibited enhanced catalytic activity towards naphthalene hydrogenation instead of cracking.For comparison,CoMoS/AC and MoS2/AC catalysts were also prepared through similar procedures,and it was found that their catalytic performance decreased in the order of NiMoS/AC〉CoMoS/AC〉MoS2/AC.Furthermore,the activity of the bimetallic NiMoS nanocatalyst can be effectively tuned via variation of the atomic ratio of Ni/（Ni＋Mo）.

Carbon dioxide reforming of methane on monolithic Ni/Al_2O_3-based catalysts

Nickel-alumina catalysts supported on cordierite monoliths of honeycomb structure surpass essentially the conventional granulated ones with respect to the output in carbon dioxide reforming of methane. Adjusting the surface acid-base properties of catalysts by introduction of alkali metal （Na, K） oxides inhibits the carbonization and as a result, improves the operational stability of these catalysts. An effect of promotion of nickel-alumina based composite doped by lanthanum oxide is found. This effect, caused by an additional route for the CO2 activation on Ni-La2O3/Al2O3/cordierite catalyst, is displayed in increase of methane conversion under conditions of an oxidant excess.

MoS_3 loaded TiO_2 nanoplates for photocatalytic water and carbon dioxide reduction

Photocatalytic water splitting and carbon dioxide reduction provide us clean and sustainable energy resources. The carbon dioxide reduction is also the redemption of the greenhouse effect. MoS/TiOphotocatalysts based on TiOnanoplates have been synthesized via a hydrothermal acidification route for water and carbon dioxide reduction reactions. This facile approach generates well dispersed Mo S3 with low crystallinity on the surface of TiOnanoplates. The as-synthesized MoS/TiOphotocatalyst showed considerable activity for both water reduction and carbon dioxide reduction. The thermal treatment effects of TiO, the loading percentage of MoSand the crystalline phase of TiOhave been investigated towards the photocatalytic performance. TiOnanoplate synthesized through hydrothermal reaction with the presence of HF acid is an ideal semiconductor material for the loading of MoSfor photocatalytic water and carbon dioxide reduction simultaneously in EDTA sacrificial solution.

The Effect of Neodymia on the Activityof Hydrocarbon Synthesis Catalysts from Carbon Dioxide

In this paper, neodymia was added into hydrocarbon synthesis catalysts by solid-mixing method to improve the activity of hydrocarbon synthesis catalyst from carbon dioxide. 0.1% Nd2O3 can improve the carbon dioxide conversion and light olefin selectivity ar 523 and 573K, but decrease the activity at 623K.

Separation and enrichment of elemental sulfur and mercury from hydrometallurgical zinc residue using sodium sulfide

The separation and enrichment of mercury and the recovery of elemental sulfur from flotation sulfur concentrate in zinc pressure leaching process were carried out by sodium sulfide leaching and carbon dioxide precipitating. The results show that the leaching rate of elemental sulfur is more than 98%, and 98.13% of mercury is enriched in the residue, under the optimized conditions of sodium sulfide concentration 1.5 mol/L, liquid/solid ratio 6：1 and leaching time 30 min at room temperature. In addition, the content of mercury is enriched 5.23 times that in the leaching residue. The elemental sulfur is precipitated from leaching solution under conditions of carbon dioxide flow rate 200 mL/min and blowing time 150 min, while solution is stirred adequately. The recovery efficiency of elemental sulfur reaches 97.67%, and the purity of elemental sulfur is 99.75%, meeting the requirements of industrial first-rate product standard according to the national standard of GB/T 2449-2006 （PRC）.

A new kinetic model for direct CO2 hydrogenation to higher hydrocarbons on a precipitated iron catalyst:Effect of catalyst particle size

The kinetic of the direct COhydrogenation to higher hydrocarbons via Fischer–Tropsch synthesis（FTS）and reverse water-gas shift reaction（RWGS） mechanisms over a series of precipitated Fe/Cu/K catalysts with various particle sizes was studied in a well mixed, continuous spinning basket reactor. The iron catalysts promoted with copper and potassium were prepared via precipitation technique in various alcohol/water mixtures to achieve a series of catalyst particle sizes between 38 and 14 nm. A new kinetic model for direct COhydrogenation was developed with combination of kinetic model for FTS reaction and RWGS equilibrium condition. For estimate of structure sensitivity of indirect COhydrogenation to higher hydrocarbons, the kinetic parameters of developed model are evaluated for a series of iron catalysts with various particle sizes. For kinetic study a wide range of syngas conversions have been obtained by varying experimental conditions. The results show that the new developed model fits favorably with experimental data. The values of activation energies for indirect COhydrogenation reaction are fall within the narrow range of 23–16 kJ/mol.

Co-CoO_x supported onto TiO_(2) coated with carbon as a catalyst for efficient and stable hydrogen generation from ammonia borane

Ammonia borane(AB) can be catalytically hydrolyzed to provide hydrogen at room temperature due to its high potentaial for hydrogen storage. Non-precious metal heterogeneous catalysts have broad application in the field of energy catalysis. In this article, catalysts precursor is obtained from Co-Ti-resorcinol-formaldehyde resin by sol–gel method. Co/TiO_(2)@N-C(CTC) catalyst is prepared by calcining the precursor under high temperature conditions in nitrogen atmosphere. Co-CoO_x/TiO_(2)@N-C(COTC) is generated by the controllable oxidation reaction of CTC. The catalyst can effectively promote the release of hydrogen during the hydrolytic dehydrogenation of AB. High hydrogen generation at a specific rate of 5905 m L min^(-1) g_(Co)^(-1) is achieved at room temperature. The catalyst retains its 85% initial catalytic activity even for its fifth time use in AB hydrolysis. The synergistic effect among Co, Co_(3)O_(4) and TiO_(2) promotes the rate limiting step with dissociation and activation of water molecules by reducing its activation energy. The applied method in this study promotes the development of non-precious metals in catalysis for utilization in clean energy sources.

Highly dispersed nickel boosts catalysis by Cu/SiO_(2) in the hydrogenation of CO_(2)-derived ethylene carbonate to methanol and ethylene glycol

The efficient hydrogenation of CO_(2)-derived ethylene carbonate(EC)to yield methanol(MeOH)and ethylene glycol(EG)is a key process for indirect conversion of CO_(2)to MeOH.However,a high H_(2)/EC molar ratio during the hydrogenation process(usually as 180-300)is generally required to achieve good catalytic performance,resulting in high cost and energy consumption for H_(2)circulation in the promising industrial application.Here,we prepared a series of Ni-modified Cu/SiO_(2)catalysts and explored the effects of synthesis methods and Ni contents on catalytic performance under different H_(2)/EC molar ratios.The Cu/SiO_(2)catalyst with 0.2%(mass)Ni loading prepared by co-ammonia evaporation method exhibited above 99%conversion of EC,91%and 98%selectivity to MeOH and EG respectively at H_(2)/EC ratio of 60.And no significant deactivation was observed within 140 h at a lower H_(2)/EC of 40.It is demonstrated that a few of Ni addition could not only promote Cu dispersion and increase surface Cu^(+) species due to the strong interaction between Cu and Ni species,but also form uniformly-dispersed CuNi alloy species and thus enhance the adsorption and dissociation of H_(2).But the excess Ni species would aggregate and segregate to cover partial surface of Cu nanoparticles,leading to a significantly drop of catalytic performance in EC hydrogenation.These insights may provide guidance for further design of catalysts for the ester hydrogenation reactions.

Effect of alkali metals on the performance of CoCu/TiO_2 catalysts for CO_2 hydrogenation to long-chain hydrocarbons

CoCu/TiO_2 catalysts promoted using alkali metals（Li, Na, K, Rb, and Cs） were prepared by the homogeneous deposition-precipitation method followed by the incipient wetness impregnation method. The influences of the alkali metals on the physicochemical properties of the CoCu/TiO_2 catalysts and the catalytic performance for CO_2 hydrogenation to long-chain hydrocarbons（C_（5＋））were investigated in this work. According to the characterization of the catalysts based on X-ray photoelectron spectroscopy, X-ray diffraction, CO_2 temperature-programmed desorption（TPD）, and H_2-TPD, the introduction of alkali metals could increase the CO_2 adsorption and decrease the H_2 chemisorption, which could suppress the formation of CH_4, enhance the production of C_（5＋）, and decrease the hydrogenation activity. Among all the promoters, the Na-modified CoCu/TiO_2 catalyst provided the maximum C_（5＋） yield of 5.4%, with a CO_2 conversion of 18.4% and C_（5＋） selectivity of42.1%, because it showed the strongest basicity and a slight decrease in the amount of H_2 desorption;it also exhibited excellent catalytic stability of more than 200 h.