Reverse water gas shift reaction over Co-precipitated Ni-CeO_2 catalysts

The Ni-CeO2 catalysts with different Ni contents were prepared by a co-precipitation method and used for Reverse Water Gas Shift （RWGS） reaction. 2wt.%Ni-CeO2 showed excellent catalytic performance in terms of activity, selectivity, and stability for RWGS reaction. Characterizations of the catalyst samples were conducted by XRD and TPR. The results indicated that, in Ni-CeO2 catalysts, there were three kinds of nickel, nickel ions in ceria lattice, highly dispersed NiO and bulk NiO. Oxygen vacancies were formed in CeO2 lattice due to the incorporation of Ni^2＋ ions into ceria lattice. Oxygen vacancies formed in ceria lattice and highly dispersed Ni were key active components for RWGS, and bulk Ni was key active component for methanation of CO2.

A Novel γ-Alumina Supported Fe-Mo Bimetallic Catalyst for Reverse Water Gas Shift Reaction

In reverse water gas shift （RWGS） reaction COa is converted to CO which in turn can be used to pro- duce beneficial chemicals such as methanol. In the present study, Mo/AlaO3, Fe/AlaO3 and Fe-Mo/Al2O3 catalysts were synthesised using impregnation method. The structures of catalysts were studied using X-ray diffraction （XRD）, Brunauer-Emmett-Teller （BET） method, inductively coupled plasma atomic emission spectrometer （ICP-AES）, temperature programmed reduction （H2-TPR）, CO chemisorption, energy dispersive X-ray （EDX） and scanning electron microscopy （SEM） techniques. Kinetic properties of all catalysts were investigated in a batch re- actor for RWGS reaction. The results indicated that Mo existence in structure of Fe-Mo/AlzO3 catalyst enhances its activity as compared to Fe/AlaO3. This enhancement is probably due to better Fe dispersion and smaller particle size of Fe species. Stability test of Fe-Mo/AlzO3 catalyst was carried out in a fixed bed reactor and a high CO yield for 60 h of time on stream was demonstrated. Fez（MoO4）3 phase was found in the structures of fresh and used catalysts. TPR results also indicate that Fez（MoO4）3 phase has low reducibility, therefore the Fe2（MoO4）3 phase significantly inhibits the reduction of the remaining Fe oxides in the catalyst, resulted in high stability of Fe-Mo/Al2O3 catalyst. Overall, this study introduces Fe-Mo/Al2O3 as a novel catalyst with high CO yield, almost no by-products and fairly stable for RWGS reaction.

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.

NiCe bimetallic nanoparticles embedded in hexagonal mesoporous silica (HMS) for reverse water gas shift reaction

Reverse water gas shift(RWGS)reaction is a crucial process in CO_(2)utilization.Herein,Ni-and NiCe-containing hexagonal mesoporous silica(Ni-HMS and NiCe-HMS)catalysts were synthesized using an insitu one-pot method and applied for RWGS reaction.At certain reaction temperatures 500-750℃,Ni-HMS samples displayed a higher selectivity to the preferable CO than that of conventionally impregnated Ni/HMS catalyst.This could be originated from the smaller NiO nanoparticles over Ni-HMS catalyst.NiCe-HMS exhibited higher activity compared to Ni-HMS.The catalysts were characterized by means of TEM,XPS,XRD,H_(2)-TPR,CO_(2)-TPD,EPR and N_(2) adsorption-desortion technology.It was found that introduction of Ce created high concentration of oxygen vacancies,served as the active site for activating CO_(2).Also,this work analyzed the effect of the H_(2)/CO_(2)molar ratio on the best NiCe-HMS.When reaction gas H_(2)/CO_(2)molar ratio was 4 significantly decreased the selectivity to CO at low temperature,but triggered a higher CO_(2)conversion which is close to the equilibrium.

The highly selective catalytic hydrogenation of CO_(2)to CO over transition metal nitrides

Three transition metal-like facet centered cubic structured transition metal nitrides,γ-Mo_(2)N,β-W_(2)N andδ-NbN,are synthesized and applied in the reaction of CO_(2)hydrogenation to CO.Among the three nitride catalysts,theγ-Mo_(2)N exhibits superior activity to target product CO,which is 4.6 and 76 times higher than the other two counterparts ofβ-W_(2)N andδ-NbN at 600℃,respectively.Additionally,γ-Mo_(2)N exhibits excellent stability on both cyclic heating-cooling and high space velocity steady state operation.The deactivation degree of cyclic heating-cooling evaluation after 5 cycles and long-term stability performance at 773 and 873 K in 50 h are all less than 10%.In-situ XRD and kinetic studies suggest that theγ-Mo_(2)N itself is able to activate both of the reactants CO_(2)and H_(2).Below 400℃,the reaction mainly occurs at the surface ofγ-Mo_(2)N catalyst.CO_(2)and H_(2)competitively adsorbe on the surface of catalyst and CO_(2)is the relatively stronger surface adsorbate.At a higher temperature,the interstitial vacancies of theγ-Mo_(2)N can be reversibly filled with the oxygen from CO_(2)dissociation.Both of the surface and bulk phase sites ofγ-Mo_(2)N participate in the high temperature CO_(2)hydrogenation pathway.