Research On Reforming Of Carbon Dioxide To Syngas Over Nickel Based Catalysts

Carbon dioxide is one of the major causes of many ecological safety issues,such as global warming and the extreme weather.CO2 reforming with CH4(CO2+CH4→2CO+2H2)not only effectively use the CO2 resources and reduce carbon emissions,but also the product,syngas(CO+H2),can be applied for the synthesis of alcohols,olefins and many other value products.Currently,the key of this reaction is to develop the special catalyst with a high catalytic activity and stability.In this study,two kinds of catalytic systems,Ni-Mg-Al with a strong basicity and Ni-Ce-Al with a strong oxygen storage,were prepared via a reflux-coprecipitation method.The effects of two different types of auxiliaries,MgO and CeO2,on CO2 reforming and carbon deposition process were discussed.In the study of the CO2-biogas reaction using a Ni-Mg-Al catalyst system,it was found that the O2 in the biogas would oxidized the active Ni metal and consequently caused a severe catalyst deactivation.Therefore,if biogas is applied to CO2 reforming process,the O2 must be removed first.In the reformation of CO2-removing biogas,the catalyst NM10 A doped with 10 mol% Mg O showed the best catalytic performance,and the conversion of CO2 and CH4 were stable at about 85%.In-situ XRD and H2-TPR showed that NM10 A contained the basic MgO and Mg Al2O4,and the metal-support is strong and no signs of free Ni O.The CO2-TPD,TEM and TGA results indicated that NM10A possessed the strongest alkalinity and the minimal carbon deposition.Based on the above characterization results,it was inferred that the addition of Mg O could enhance the alkalinity of the catalyst and consequently promoted the ability of CO2 adsorption and activation,resulting in the more oxygen species and therefore accelerated carbon releasing.In the Mg-containing catalyst,a micro-composite oxide with an oxygen-storage ability was also formed.In order to study the influence of oxygen storage performance on catalytic activity and carbon deposition in detail,selecting the rare earth metal oxide CeO2 with a special oxidation-reduction property and a strong oxygen-storage ability to modify the Ni-Al catalyst system.In the study of CO2-natural gas using a Ni-Ce-Al catalyst system,it was found that Ni10CeAl doped with 10 mol% Ni showed the best catalytic performance,and the CO2 and CH4 conversion were also stable at about 85%.In-situ XRD and H2-TPR showed the coexistence of various Ce oxides(CeO2,Ce2O3 and Ce Al O3)in the catalyst.TEM and TGA results showed that reacted Ni10 Ce Al contained a small amount of amorphous carbon and filamentous carbon and no graphite carbon was detected.The former two have little effects on the catalytic activity but graphite carbon was the main cause of catalyst deactivation.The above characterization results implied that the coexistence of CeO2,Ce2O3 and CeAlO3 caused the oxygen vacancies on the surface of the catalyst,resulting in a strong oxygen storage capacity to accelerate the consumption of carbon species.Meanwhile,it could inhibit effectively the generation of graphitic carbon and therefore prevented the catalyst deactivation.