An investigation of Zr/Ce ratio influencing the catalytic performance of CuO/Ce1-xZrxO2 catalyst for CO2 hydrogenation to CH3OH

A series of CuO/Ce1-xZrxO2 catalysts(x=0.2,0.4,0.6 and 0.8)are applied to elaborate the effect of the Zr/Ce ratio on the catalytic performance of CO2 hydrogenation to CH3OH.The best catalytic performance is achieved with CuO/Ce0.4Zr0.6O2,exhibiting XCO2=13.2%and YCH3OH=9.47%(T=280℃,P=3 MPa).The formation of dispersed surface CuO species and larger number of oxygen vacancies are detected over CuO/Ce0.4Zr0.6O2 due to stronger interaction between CuO and Ce0.4Zr0.6O2,resulting in the superior activation ability for H2 and CO2 respectively.Additionally,the evidence is provided by in situ DRIFTS under the activity test pressure(3 MPa)that bi/m-HCOO* species are preferable for accumulating over ceria-rich(CuO/Ce0.6Zr0.4O2 and CuO/Ce0.8Zr0.2O2)catalysts while zirconia-rich(CuO/Ce0.4Zr0.6O2 and CuO/Ce0.2Zr0.8O2)catalysts are benefit to encourage the transformation of bi/m-HCOO* species to CH3OH.The abundant population and high activity of intermediate species over CuO/Ce0.4Zr0.6O2 give a strong positive effect on the catalytic performance.

Selective hydrogenation of CO2 to methanol over Ni/In2O3 catalyst

An In2O3 supported nickel catalyst has been prepared by wet chemical reduction with sodium borohydride(NaBH4) as a reducing agent for selective hydrogenation of carbon dioxide to methanol. Highly dispersed Ni species with intense Ni-In2O3 interaction and enhanced oxygen vacancies have been achieved.The highly dispersed Ni species serve as the active sites for hydrogen activation and hydrogen spillover.Abundant H adatoms are thereby generated for the oxygen vacancy creation on the In2O3 surface. The enhanced surface oxygen vacancies further lead to improved CO2 conversion. As a result, an effective synergy between the active Ni sites and surface oxygen vacancies on In2O3 causes a superior catalytic performance for CO2 hydrogenation with high methanol selectivity. Carbon monoxide is the only by product detected. The formation of methane can be ignored. When the reaction temperature is lower than 225 ℃,the selectivity of methanol is 100%. It is higher than 64% at the temperature range between 225 ℃ and 275 ℃. The methanol selectivity is still higher than 54% at 300 ℃ with a CO2 conversion of 18.47% and a methanol yield of 0.55 gMeOHg-1cath-1(at 5 MPa). The activity of Ni/In2O3 is higher than most of the reported In2O3-based catalysts.

Active sites in CO2 hydrogenation over confined VOx-Rh catalysts

Metal oxide-promoted Rh-based catalysts have been widely used for CO2 hydrogenation,especially for the ethanol synthesis.However,this reaction usually suffers low CO2 conversion and alcohols selectivity due to the formation of byproducts methane and CO.This paper describes an efficient vanadium oxide promoted Rh-based catalysts confined in mesopore MCM-41.The Rh-0.3VO/MCM-41 catalyst shows superior conversion(〜12%)and ethanol selectivity(〜24%)for CO2 hydrogenation.The promoting effect can be attributed to the synergism of high Rh dispersion by the confinement effect of MCM-41 and the formation of VOr-Rh interface sites.Experimental and theoretical results indicate the formation of til-CO at VOv-Rh interface sites is easily dissociated into*CH X,and then*CH X can be inserted by CO to form CH3,*CO followed by CH3*CO hydrogenation to ethanol.

Mechanism and catalytic performance for direct dimethyl ether synthesis by CO2 hydrogenation over CuZnZr/ferrierite hybrid catalyst

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.

Structural properties and catalytic performance of the La-Cu-Zn mixed oxides for CO2 hydrogenation to methanol

A series of La-Cu-Zn-O mixed oxide catalysts were synthesized by a co-precipitation method and calcined under different temperatures. The XRD, BET, TPR, N2 O-adsorption, XPS, SEM and TPD techniques were carried out to measure the aimed catalysts. The results indicated that the chemical environment of lanthanum element changes with the increase of calcination temperature. The La2 CuO4 perovskite structure is obtained at the temperature higher than 823 K and the special copper species appear in the perovskites due to the special structure property. The catalysts with La2 CuO4 perovskite structure show higher methanol selectivity compared with the mixed copper catalyst. For the perovskite catalysts, the conversion of CO2 changes with the same tendency of the copper species ratio（（Cu^（α＋）＋Cu^0）/（Cu（Total））%）, which implied both Cu^（α＋） and Cu^0 are important active sites in the perovskite catalyst for the reaction.

Preparation and Characterization of SiO2/Co and C/Co Nanocomposites as Fisher-Tropsch Catalysts for CO2 Hydrogenation

To fabricate high-density cobalt-based catalysts, we first synthesized SiO]C composites via a hydrother- mad method and removed C and SiO2 by two different methods, respectively. The as-prepared SiO2 and C supports then reacted with cobalt acetylacetonate and N,N-dimethylformamide（DMF） under hydrothermal conditions to prepare SiO2/Co and C/Co nanocomposite catalysts. The catalysts were characterized by X-ray difffaction（XRD）, scanning electron microscope（SEM）, transmission electron microscopy（TEM）, inductively coupled plasma mass spectrometry（ICP）~ energy dispersive X-ray fiuoresence spectrometer（EDX）, and nitrogen adsorption. It was found that hexagonal cobalt nanocrystals were successfully integrated with the mesoporous silica or carbon nanotube supports. SEM and TEM results show that SiO2/Co composites with a hollow/mesoporous sphere structure and C/Co composites with a tubular structure have been successfully synthesized. Both composite samples show superpara- magnetism exhibiting an S-type hysteresis loop, which originated from the cobalt nanoparticles in the samples. Nitrogen adsorption/desorption curves suggest that the SiO2 and C supports have well-developed pore structures and large specific surface areas, and the loading and good dispersity of cobalt nanoparticles on the supports were proven by ICP and EDX. Moreover, the samples exhibited good and stable catalytic activity, denlonstrating that the two composites are suitable catalysts for Fischer-Tropsch CO2 hydrogenation.

Effects of ZrO_2 on the Performance of CuO-ZnO-Al_2O_3/HZSM-5 Catalyst for Dimethyl Ether Synthesis from CO_2 Hydrogenation

A series of composite catalysts were prepared by the wet mixing method, and the mass ratio of CuO-ZnO-Al2O3-ZrO2 component to HZSM-5 zeolite （molar ratio of SiO2 to Al2O3 being 25） was 2：1. The CuO-ZnO-Al2O3-ZrO2 （CuO/ZnO/Al2O3=3/6/1 by weight） component was prepared by a modified ＇two-step＇ co-precipitation method. The effects of ZrO2 on the performance of CuO-ZnO-Al2O3/HZSMo5 catalyst for dimethyl ether synthesis from CO2 hydrogenation were investigated. It was found that ZrO2 improved the properties of CuO-ZnO-Al2O3/HZSM-5 as a structural promoter.

Ti-Si composite oxide-supported cobalt catalysts for CO_2 hydrogenation

In the present work, different silica-based supported cobalt （Co） catalysts were synthesized and used for CO2 hydrogenation for methanation. Different supports, such as SSP, MCM-41, TiSSP and TiMCM were used to prepare Co catalysts with 20 wt% Co loading. The supports and catalysts were characterized by means of N2 physisorption, XRD, SEM/EDX, XPS, TPR and CO chemisorption. It is found that after calcination of catalysts, Ti is present in the form of anatase. The introduction of Ti plays important roles in the properties of Co catalysts by：（i） facilitating the reduction of Co oxides species which are strongly interacted with support, （ii） preventing the formation of silicate compounds, and （iii） inhibiting the RWGS reaction. Based on CO2 hydrogenation, the CoTiMCM catalyst exhibites the highest activity and stability.

The thermodynamics analysis and experimental validation for complicated systems in CO_2 hydrogenation process

Catalytic conversion of COinto chemicals and fuels is an alternative to alleviate climate change and ocean acidification.The catalytic reduction of COby Hcan lead to the formation of various products:carbon monoxide,carboxylic acids,aldehydes,alcohols and hydrocarbons.In this paper,a comprehensive thermodynamics analysis of COhydrogenation is conducted using the Gibbs free energy minimization method.The results show that COreduction to CO needs a high temperature and H/COratio to achieve a high COconversion.However,synthesis of methanol from COneeds a relatively high pressure and low temperature to minimize the reverse water-gas shift reaction.Direct COhydrogenation to formic acid or formaldehyde is thermodynamically limited.On the contrary,production of CHfrom COhydrogenation is the thermodynamically easiest reaction with nearly 100%CH4 yield at moderate conditions.In addition,complex reactions with more than one product are also calculated in this work.Among the considered carboxylic acids（HCOOH,CHCOOH and CHCOOH）,propionic acid dominates in the product stream（selectivity above 90%）.The same trend can also be found in the hydrogenation of COto aldehydes and alcohols with the major product of propionaldehyde and butanol,respectively.In the process of COhydrogenation to alkenes,low temperature,high pressure,and high Hpartial pressure favor the COconversion.CHis the most thermodynamically favorable among all considered alkynes under different temperatures and pressures.The thermodynamic calculations are validated with experimental results,suggesting that the Gibbs free energy minimization method is effective for thermodynamically understanding the reaction network involved in the COhydrogenation process,which is helpful for the development of high-performance catalysts.

Characterization and performance of Cu/ZnO/Al_2O_3 catalysts prepared via decomposition of M(Cu,Zn)-ammonia complexes under sub-atmospheric pressure for methanol synthesis from H_2 and CO_2

Methanol synthesis from hydrogenation of CO2 is investigated over Cu/ZnO/Al2O3 catalysts prepared by decomposition of M（Cu,Zn）-ammonia complexes （DMAC） at various temperatures.The catalysts were characterized in detail,including X-ray diffraction,N2 adsorption-desorption,N2O chemisorption,temperature-programmed reduction and evolved gas analyses.The influences of DMAC temperature,reaction temperature and specific Cu surface area on catalytic performance are investigated.It is considered that the aurichalcite phase in the precursor plays a key role in improving the physiochemical properties and activities of the final catalysts.The catalyst from rich-aurichalcite precursor exhibits large specific Cu surface area and high space time yield of methanol （212 g/（Lcat·h）;T=513 K,p=3MPa,SV=12000 h-1）.

Dimethyl ether synthesis from CO_2 hydrogenation on La-modified CuO-ZnO-Al_2O_3 /HZSM-5 bifunctional catalysts

A series of CuO-ZnO-Al2O3-La2O3/HZSM-5 biftmctional catalysts with various La loadings for dimethyl ether （DME） directly synthesized from CO2 hydrogenation were prepared. The catalysts were characterized with N2 adsorption-desorption, X-ray diffraction （XRD）, H2 temperature-programmed reduction （H2-TPR）, NH3 temperature-programmed desorption （NH3-TPD） and N2O titration techniques, and tested for the synthesis of DME directly from CO2 hydrogenation in a fixed-bed reactor. The results showed that the reducibility, dispersion ofbifunctional catalysts were strongly dependent on the addition of La. With the addition of appropri- ate amount of La, the crystaUite size of CuO was decreased and the dispersion of Cu on the surface was enhanced, which resulted in the increased conversion of CO2. It was also found that the selectivity to DME was related to the intensity and amount of strong acid site on the catalyst surface. The presence of La favored the production of DME, and the optimum catalytic activity was obtained when the amount of La was 2.0 wt.%.

Morphology and activity relationships of macroporous CuO-ZnO-ZrO_2 catalysts for methanol synthesis from CO_2 hydrogenation

A series of macroporous CuO-ZnO-ZrO2 （CZZ） catalysts with different Zn/Zr ratios were successfully prepared by template method and characterized by X-ray diffraction （XRD）, N2 adsorption, reactive N2O adsorption, scanning electron microscopy （SEM）, H2 temperature-pro- grammed reduction （H2-TPR）, and transmission electron microscopy （TEM）. The activity of the catalysts was tested for methanol synthesis from CO2 hydrogenation. It is found that the increase in the Zn/Zr ratio could lead to the sintering of the catalysts, destroying the macroporous structure integrity. The macroporous CZZ catalysts own lower Zn/Zr ratio, exhibiting a better morphology and activity. For comparison, the conventional nonporous CZZ catalysts were also investigated. The results show that the CZZ catalysts with macroporous structure own smaller particles, higher CO2 conversion, and CH3OH yield. It reveals that the macroporous structure could inhibit the growth of the par- ticle size, and the special porous structure is favorable for diffusion and penetration of CO2, which could improve the catalytic activities.

Influence of copper content on structural features and performance of pre-reduced LaMn_(1-x)Cu_xO_3 (0≤x<1) catalysts for methanol synthesis from CO_2/H_2

A series of pre-reduced LaMn1–xCuxO3 (0≤x<1) catalysts for methanol synthesis from CO2 hydrogenation were prepared by a sol-gel method. The catalytic performances were strongly dependent on the copper content. XRD investigation revealed that the single perovskite structure could be preserved after being reduced, when the substitution for Mn by Cu was less than 50%. The Cu-doped (x=0.5) LaMnO3 was much more active than the other catalysts for reaction, showing CO2 conversion up to 11.33% and methanol sele...