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.

Total entropy generation rate minimization configuration of a membrane reactor of methanol synthesis via carbon dioxide hydrogenation

The total entropy generation rate,internal exergy loss and exergy efficiency of the membrane reactor of methanol synthesis via carbon dioxide hydrogenation are compared,and the results show that the total entropy generation rate minimization is equivalent to the internal exergy loss minimization and the exergy efficiency maximization under the fixed inlet exergy.Therefore,this paper optimizes the membrane reactor with total entropy generation rate minimization as an optimization objective under a fixed methanol production rate.The optimal temperatures curves of exterior walls for three optimal membrane reactors with different boundary conditions are obtained by using optimal control theory and nonlinear programming.The influences of other geometric and operating parameters on optimization results of optimal membrane reactors are analyzed.The results indicate that when inlet temperatures of the reaction mixture and mixture in the permeable tube are unfixed,the optimizing curve of exterior wall temperature makes the total entropy generation rate of membrane reactor reduce by 12.39%compared with the total entropy generation rate of a reference membrane reactor with a linear exterior wall temperature.Decreasing the inlet molar flow rate of sweep gas and gas hourly space velocity and increasing inlet pressure of reaction mixture,the inlet pressure of mixture in the permeable tube and heat transfer coefficients are favorable for decreasing the total entropy generation rate in the membrane reactor.As the porosity of catalyst bed and reactor length increases,the minimum total entropy generation rate decreases first and then increases.From the perspective of engineering application,this paper establishes two membrane reactors(membrane reactor heated by three-stage furnaces of the same length and membrane reactor heated by threestage furnaces of different lengths),respectively.The minimum total entropy generation rates of the two reactors are reduced by11.67%and 11.79%compared with the total entropy generation rate in the reference membrane reactor,respectively.The obtained results are beneficial to the optimal design of energy-efficient membrane reactors.

Experimental investigation on the origin of carbonaceous materials in the fault zone of the Wenchuan earthquake

Carbonaceous materials in seismic fault zones may considerably influence seismic fault slip;however,the formation mechanism of carbonaceous materials remains unclear.In this study,we proposed a novel hypothesis for the formation of carbonaceous materials in fault gouge.Thus,we conducted a CO_(2) hydrogenation experiment in a high-temperature reactor at a co-seismic temperature,with fault gouge formed during the Wenchuan earthquake as the catalyst.Our experimental results demonstrate that carbonaceous materials in fault zones are formed on the fault gouge during the chemical reaction process,suggesting that the carbonaceous materials are possibly generated from the catalytic hydrogenation of CO_(2),followed by thermal cracking of its products.The results of this study provide a theoretical basis for understanding fault behavior and earthquake physics.

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.

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.

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.

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.

CO_2 hydrogenation to methanol over Cu/Zn/Al/Zr catalysts prepared by liquid reduction

Cu/Zn/Al/Zr catalysts containing Cu in three valence states(Cu2+,Cu+and Cu0)were prepared usinga liquid reduction method and subsequently calcined at different temperatures.The effects of thecalcination temperature on the catalyst structure,interactions among components,reducibility anddispersion of Cu species,surface properties and exposed Cu surface area were systematically investigated.These materials were also applied to the synthesis of methanol via the hydrogenation ofCO2.The results show that a large exposed Cu surface area promotes catalytic CO2conversion andthat there is a close correlation between the Cu+/Cu0ratio and the selectivity for methanol.A calcinationtemperature of573K was found to produce a Cu/Zn/Al/Zr catalyst exhibiting the maximumactivity during the synthesis of methanol.

Effect of In_(2)O_(3)particle size on CO_(2) hydrogenation to lower olefins over bifunctional catalysts

A reaction-coupling strategy is often employed for CO_(2)hydrogenation to produce fuels and chemicals using oxide/zeolite bifunctional catalysts.Because the oxide components are responsible for CO_(2)activation,understanding the structural effects of these oxides is crucial,however,these effects still remain unclear.In this study,we combined In_(2)O_(3),with varying particle sizes,and SAPO‐34 as bifunctional catalysts for CO_(2)hydrogenation.The CO_(2)conversion and selectivity of the lower olefins increased as the average In_(2)O_(3)crystallite size decreased from 29 to 19 nm;this trend mainly due to the increasing number of oxygen vacancies responsible for CO_(2) and H_(2) activation.However,In_(2)O_(3)particles smaller than 19 nm are more prone to sintering than those with other sizes.The results suggest that 19 nm is the optimal size of In_(2)O_(3)for CO_(2)hydrogenation to lower olefins and that the oxide particle size is crucial for designing catalysts with high activity,high selectivity,and high stability.

Theoretical Investigation for Two-state Reactivity of CO_2 Hydrogenation Catalyzed by Ru in Gas Phase

Gas-phase CO_2 catalyzed activation hydrogenation by Ru atoms was studied with density functional theory. Based on the structure optimization of different potential energy surfaces,there are two crossing points between singlet and triplet potential energy surfaces and there is a crossing point between quintet and triplet potential energy surfaces in the whole catalytic cycle. Spin transition probabilities in the vicinity of the intersections have been calculated by the Landau-Zener model theory. There are three minimum energy crossing points（MECPs） with strong spin-orbital coupling effect and higher spin transition probability,and all spin inversion occurred in s orbital and different d orbitals of ruthenium,indicating this is a typical two-state reactivity（TSR） reaction. Finally,the lowest energy reaction path is ensured.

Simultaneous recovery of carbon and sulfur resources from reduction of CO_2 with H_2S using catalysts

An approach to the simultaneous reclamation of carbon and sulfur resources from CO2 and H2S has been proposed and effectively implemented with the aid of catalysts. A brief thermodynamic study reveals the potential of direct reduction of CO2 with H2S（15：15 mol% balanced with N2） for selective production of CO and elemental sulfur. The experiments carried out in a fixed-bed flow reactor over the temperature range of 400–800 °C give evidence of the importance of the employment of catalysts. Both the conversions of the reactants and the selectivities of the target products can be substantially promoted over most catalysts studied. Nevertheless, little difference appears among their catalytic performance. The results also prove that the presence of CO2 can remarkably enhance H2S conversion and the sulfur yield in comparison with H2S direct decomposition. A longtime reaction test on Mg O catalyst manifests its superior durability at high temperature（700 °C） and huge gas hourly space velocity（100,000 h-1）. Free radicals initiated by catalysts are supposed to dominate the reactions between CO2 and H2S.

Selective synthesis of carbon monoxide via formates in reverse water–gas shift reaction over alumina-supported gold catalyst

Thermal decomposition of formic acid on SiO2, CeO2 and γ-Al2O3 was studied as an elementary step of reverse water–gas shit reaction（RWGS） over supported Au catalysts. γ-Al2O3 showed the highest CO selectivity among the tested oxides in the decomposition of formic acid. Infrared spectroscopy showed the formation of four formate species on γ-Al2O3： three η~1-type and one μ~2-type species, and these formates decomposed to CO at 473 K or higher. Au-loaded γ-Al2O3 samples were prepared by a depositionprecipitation method and used as catalysts for RWGS. The supported Au catalyst gave CO with high selectivity over 99% from CO2 and H2, which is attributed to the formation of formates on Au and subsequent decomposition to CO on γ-Al2O3.

Nickel-modified In_(2)O_(3) with inherent oxygen vacancies for CO_(2) hydrogenation to methanol

Methanol synthesis is one of the most important industrially-viable approaches for carbon dioxide(CO_(2)) utilization, as the produced methanol can be used as a platform chemical for manufacturing green fuels and chemicals. The In_(2)O_(3) catalysts are ideal for sustainable methanol synthesis and have received considerable attention. Herein, Co-, Ni-and Cu-modified In_(2)O_(3) catalysts were fabricated with high dispersion and high stability to improve the hydrogenation performance. The Ni-promoted In_(2)O_(3) catalyst in the form of high dispersion possessed the largest amount of oxygen vacancies and the strongest ability for H_(2) activation, leading to the highest CO_(2) conversion and space time yield of methanol of 0.390 g_(Me OH)g_(cat)^(-1)h^(-1) with CH_(3)OH selectivity of 68.7%. In addition, the catalyst exhibits very stable performance over 120 h on stream, which suggests the promising prospect for industrial applications. Further experimental and theoretical studies demonstrate that surface Ni doping promotes the formation of oxygen defects on the In_(2)O_(3) catalyst, although it also results in lower methanol selectivity. Surprisingly, subsurface Ni dopants are found to be more beneficial for methanol formation than surface Ni dopants, so the Nipromoted In_(2)O_(3)catalyst with a lower surface Ni content at the similar Ni loading can reach higher methanol selectivity and productivity. This work thus provides theoretical guidance for significantly improving the CO_(2) reactivity of In_(2)O_(3)-based catalysts while maintaining high methanol selectivity.

Designing of highly selective and high-temperature endurable RWGS heterogeneous catalysts: recent advances and the future directions

Reverse water gas shift（RWGS） reaction can be served as a pivotal stage of transitioning the abundant CO;resource into chemicals or hydrocarbon fuels, which is attractive for the CO;utilization and of eventually significance in enabling a rebuilt ecological system for unconventional fuels. This concept is appealing when the process is considered as a solution for the storage of renewable energy, which may also find a variety of potential end uses for the outer space exploration. However, a big challenge to this issue is the rational design of high temperature endurable RWGS catalysts with desirable CO product selectivity. In this work, we present a comprehensive overview of recent publications on this research topic,mainly focusing on the catalytic performance of RWGS reaction over three major kinds of heterogeneous catalysts, including supported metal catalysts, mixed oxide catalysts and transition metal carbides. The reaction thermodynamic analysis, kinetics and mechanisms are also described in detail. The present review attempts to provide a general guideline about the construction of well-performed heterogeneous catalysts for the RWGS reaction, as well as discussing the challenges and further prospects of this process.

Highly efficient Cu/anatase TiO2 {001}-nanosheets catalysts for methanol synthesis from CO2

Anatase TiO2 nanosheets（-ns-） with dominant exposed {001} facets were used as support to load copper,and the synthesized Cu/TiO2-ns catalysts were evaluated for CO2 hydrogenation to methanol. Under the reaction conditions, P = 3.0 MPa, T = 260 ℃, V（N2）：V（H2）：V（CO2） = 8：69：23 and gas hourly space velocity（GHSV） = 3600 mL g-1h-1, the methanol yield reached an appealing high value, 5.6%. Copper-loading amount, calcination temperature and reduction atmosphere have been investigated in this work, which significantly influence the particle sizes of copper and/or the defect concentration in TiO2, then leading to different catalytic performance. Characterizations of XRD, EPR, CO2-TPD and FTIR demonstrate that higher specific surface area of Cu is good for the hydrogenation of CO2 and adequate amount of Ti3＋ plays important roles in CO2 activation. Both of them facilitate high turnover frequency（TOF） of methanol formation.

Identification of photochemical effects in Ni-based photothermal catalysts

Photochemical catalytic processes can reduce the activation energy so that reactions can occur under milder conditions.However,it is still unknown whether photochemical effects are present in photothermal catalysis over conventional transition metal materials.Herein,the representative photothermal CO_(2)hydrogenation catalyst,Ni@p-SiO_(2),is employed as a model system to quantitatively probe the contribution of photochemical effect.Through a series of catalytic and photophysical characterizations,it is found that negligible photochemical effect in the ultraviolet-visible region can be observed for the traditional Ni-based catalyst.The results of photo-electrochemistry(PEC)test further confirm that no apparent photochemical effect is present for the Ni@p-SiO_(2)catalyst in the aqueous-phase environment.It has been further evidenced that the photochemical contributions can be significantly amplified by introducing plasmonic metals,such as Au,into the system.This work provides a guideline for the design and construction of efficient synergetic photothermal-photochemical catalytic systems.

N-methylation of quinolines with CO2 and H2 catalyzed by Ru-triphos complexes

N-methyl-tetrahydroquinolines(MTHQs) are a kind of very useful chemicals, which can be obtained from N-methylation of amines.However, the methylation of quinolines which is a kind of highly unsaturated nitrogen-containing heterocyclic aromatic compounds has not been reported. In this work, we report the first work for the synthesis of MTHQs by methylation of quinolines using CO_2 and H_2. It was found that Ru(acac)_3-triphos [triphos: 1,1,1-tris(diphenylphosphinomethyl)ethanl] complex was very active and selective for the N-methylation reaction of quinolines, and the yield of the desired product could reach 99%.