Hydrogenation Of CO/CO₂ To Methane Over Ni-based Catalysts Derived From Pervoskite

Owing to the energy structural characteristics of"rich coal,poor oil and little gas"in our country and the state of the greenhouse gas CO₂ emission,and the potential application of methane in fuel or chemical intermediates,methane synthesis from coal or biomass via syngas has important strategic significance and potential applications prospect.Meanwhile,the carbon dioxide hydrogenation to produce methane can provide inspiration for the problem of hydrogen storage,in addition to mitigating environmental problems.In this paper,based on the structure characteristic of the perovskite-type-oxides and the problems faced for the catalysts,we have designed and prepared a series of LaNiO₃/SiO₂,LaRu_xNi_1-xO₃/SiO₂,LaNi_1-xMo_xO₃/SiO₂,and La_1-xCe_xNiO₃/ZrO₂ catalyst precursors with special structures and compositions.Using LaNiO₃ with perovskite structure as the precursor loaded on SiO₂ by the citrate complexing method,the catalyst of Ni/La₂O₃/SiO₂ was produced after reduction,and their catalytic performances were measured for CO methanation from syngas to generate CH₄.The prepared catalyst derived from LaNiO₃/SiO₂showed very good catalytic performance,especially showed very high resistance towards carbon deposition and nickel sintering,which is better than NiO-La₂O₃/SiO₂ prepared by common incipient-wetness impregnation method.This is because,in Ni/La₂O₃/SiO₂ derived from LaNiO₃/SiO₂,Ni nanoparticles are close to La₂O₃ and confined by La₂O₃ which are spread on SiO₂.The noble metal Ru is an active component with excellent activity for CO methanation,but its wide application was restricted by the high price.Here,the perovskite-type oxide precursor of LaRu_xNi_1-xO₃ was made by impregnation method.By reducing the catalysts with hydrogen,bimetallic nanoparticles with the structure of nickel shell and ruthenium core of Ru@Ni supported on SiO₂ doped with La₂O₃ were made,and the Ru would migrate to the surface of the Ni-Ru cluster forming the ruthenium shell and nickel core of Ni@Ru under CO atmosphere.The supported bimetal catalysts with core-shell structure by doping small amount of noble metal exhibited very good catalytic performance for CO methanation,especially showed excellent resistance to carbon deposition and metal sintering,while the monometallic catalyst of nickel showed inferior catalytic performance.The excellent performance could attribute to the high metal dispersion and high utilization efficiency of noble metal.The preparation scheme for the core-shell structure of non-noble@noble/support can be extended to design and prepare other bimetallic nano-materials.The crucial problems for the catalysts of CO₂ methanation are the low activity at low temperature and deactivation caused by metal sintering.Starting from the reaction methanism,a new scheme has been put forward by loading LaNi_1-xMo_xO₃ with perovskite-type structure on SiO₂.After reduction,Ni nanoparticles,MoO_x and La₂O₃ would be all stay together and highly dispersed on SiO₂(Ni/MoO_x-La₂O₃/SiO₂).The resultant Ni/MoO_x-La₂O₃/SiO₂ catalyst exhibited pretty good performance for CO₂ methanation comparing with Ni-La₂O₃/SiO₂ catalyst without adding Mo,especially showing very good resistance to metal sintering.This is because the MoO_x species can convert CO₂ to CO by RWGS and then CO methanation might happen on the adjacent Ni nano particles,that is to say,Ni,MoO_xand La₂O₃ are always in close touch.In order to improve the activity of CO₂ methanation at low temperature,a new catalyst of cerium modified Ni-La₂O₃/ZrO₂ was prepared by using La_1-xCe_xNiO₃/ZrO₂ with perovskite phase as the precursor,which was obtained according to citrate complexation combined with impregnation method,and the catalytic performances for CO₂ methanation was investigated.Cerium modifying could improve the effective activation of CO₂,thus enhancing the activity at low temperature for CO₂ methanation.The metal Ni nanoparticles prepared according to this method are highly dispersed and show excellent resistance to sintering,leading to very good stability.