Highly Efficient Anti-carbon Deposition Ni_10.7Y_xW_y/?-Al₂O₃ Catalyst In Methane Dry Reforming

The main component of natural gas,shale gas and natural gas hydrate is CH₄,and CH₄ is a clean energy source.The main component of greenhouse gases is CO₂.Methane dry reforming with another greenhouse gas carbon dioxide?DRM?can be used to lower the greenhouse effect and produce high-value-added syngas.Syngas,the mixture of gases with different ratios of CO and H₂,could be used as the raw material to produce liquid fuels and important chemicals through Fischer-Tropsch?FT?synthesis.In recent decades,nickel-based catalysts have been extensively studied,especially Ni/Al₂O₃ catalysts.These nickel-based catalysts are inexpensive,easy to produce,have similar catalytic activity to precious metals,and have lower operating costs.Firstly,the catalytic performance of Ni/?-Al₂O₃ catalyst was studied.The effects of the loading of active components,reaction temperature and weight hourly space velocity on the catalytic activity were investigated.The optimum nickel loading was10.7%,the optimum reaction temperature was 800?,and the optimum weight hourly space velocity was 96 000 mL/?h·g?.Ni/?-Al₂O₃ catalysts were prepared by deposition precipitation method?DP?,co-precipitation method?CP?and incipient wetness co-impregnation?IWI?.The performance of dry reforming reaction and phase structure?XRD?were characterized.It was found that the catalyst prepared by the sedimentation precipitation method has the best activity and stability,while the catalyst prepared by the incipient wetness co-impregnation method has the worst activity and stability,but the molar ratio of hydrogen to carbon monoxide is the largest,close to 1,which is the most ideal.Secondly,we prepared a series of Ni_10.7Y_x/?-Al₂O₃?x=0,3,5,10,20 wt%?catalysts by incipient wetness co-impregnation method,and determined the series according to the reaction conditions explored above.The catalysts before and after the reaction were tested by BET,H₂ pulse adsorption,XRD,H₂-TPR,TG-DSC,HRTEM,TPH and FT-IR characterization methods.The results show that the Ni_10.7Y₃/?-Al₂O₃catalyst has the highest methane conversion rate?84.5%?due to the high dispersion of the active components of the catalyst.The introduction of Y₂O₃ weakens the interaction between NiO and Al₂O₃ or NiAl₂O₄.When Y loading exceeds 10%,Y inhibits the formation of NiAl₂O₄.The sintering of Ni0 particle size and the accumulation of filamentous carbon deposits are the main reasons leading to the deactivation of the final catalytic activity of the Ni_10.7/?-Al₂O₃ catalyst during the DRM reaction.The experimental team found that the N Ni_10.7Y_x/?-Al₂O₃?x>0?catalyst has good carbon deposition resistance.The amount of filamentous carbon gradually decreased with the increase in Y content.Y₂O₃ interacted with CO₂ to form Y₂O₂CO₃ which inhibited the formation of filamentous carbon by blocking the migration of carbon deposition in Ni particles during the DRM reaction.Finally,we prepared a series of Ni_10.7W_y/?-Al₂O₃?x=0,5.9,10,15,20 wt%?catalysts by incipient wetness co-impregnation method.Through the DRM catalytic reaction test,the experimental team found that Ni_10.7W₁₀/?-Al₂O₃ has the highest initial methane conversion rate and is the most stable in the 30 h DRM stability test.Through the above-mentioned DRM test and some characterization methods,we found that the optimum loadings were 3%and 10%,respectively,through the above-mentioned different loadings of rare earth metal element Y and transition metal element W.In order to further explore the catalytic performance of the catalysts added by the two additives to the DRM reaction,a series of Ni_10.7Y_xW_y/?-Al₂O₃ catalysts were prepared by the incipient wetness co-impregnation method for dry reforming of methane carbon dioxide?DRM?.The catalysts were characterized by XRD,BET,H₂-TPR,TPH,HRTEM and XPS.The effects of metal promoters on the performance of the catalysts were investigated.The results showed that the addition of yttrium enhanced the degree of reduction of NiAl₂O₄ and promoted the dispersion of the active component Ni.The addition of yttrium and tungsten could reduce the specific surface area,pore size and pore volume of the catalyst.The stability of Ni_10.7Y₃W₁₀/?-Al₂O₃ catalyst was the best.During the DRM reaction,the formation of Y₂O₂CO₃ by the interaction of Y₂O₃ and CO₂ could inhibit the formation of filamentous carbon,thereby improving the activity and stability of the catalyst.The Ni_10.7W₁₀/?-Al₂O₃ catalyst underwent W carbonization reaction to form?-WC during the DRM reaction,which forms a double active site with the active component Ni,thereby improving the activity and stability of the catalyst.The Ni_10.7Y₃W₁₀/?-Al₂O₃catalyst not only generated double active sites,but also effectively inhibited the diffusion of carbon deposits,thereby inhibiting the formation of filamentous carbon.