Supercritical Hydrothermal Preparation Of Nano-Ni-based Catalyst And Its Catalytic Performance In Supercritical Water Gasification Of Biomass

Realizing the efficient conversion and utilization of renewable biomass energy has always been a research hotspot.As a new hydrogen production technology,supercritical water gasification of biomass has a good application prospect.However,the catalyst prepared by conventional method has a problem of sintering deactivation in supercritical water gasification.In this paper,a new research idea of using nanoparticles of supercritical hydrothermal synthesis as a supercritical water gasification catalyst is proposed.The supercritical hydrothermal synthesis of nickel catalysts and the catalytic performance of supercritical water gasification are studied.The support materials of nickel are screened,and the influence of thermal and mass parameters on the performance of synthetic particles in the continuous supercritical hydrothermal synthesis process,which provided a certain research basis for the use of supercritical hydrothermal controllable synthesis of high-performance supercritical water gasification catalysts.Firstly,Al₂O₃,Mg modified Al₂O₃,ZrO₂,Ce modified ZrO₂,active carbon（AC）and carbon nanotubes（CNT）were selected as support materials,and a series of supported Ni particles were prepared by supercritical hydrothermal synthesis.The catalytic activity and hydrothermal stability of the nanoparticles were evaluated in the supercritical water gasification of glycerol.The results showed that Mg modified Al₂O₃ supported nickel catalyst exhibited high catalytic activity comparable to that of sol-gel catalyst.However,the Ni/Mg-Al-O catalyst prepared by supercritical hydrothermal synthesis exhibited more excellent crystal phase structure and pore structure stability and better renewable activity,which verified the feasibility of the new research ideas proposed in this paper.Furthermore,with Ni/Mg-Al-O particles as the research object,the effects of synthesis temperature,synthesis reaction heating time and precursor concentration on the performance of the synthesized particles were systematically investigated in the continuous supercritical hydrothermal synthesis reaction.The results showed that when the synthesis temperature increased to 500°C,the conversion of Ni component precursor increased to about 95%;with the increase of synthesis temperature,the fusiform particles formed by the bonding of flakes gradually became needle like particles with high dispersion and uniform particle size;with the increase of reaction heating time,the composite particles were formed by the adhesion and recrystallization of fine and highly dispersed primary particles;the increase of Al component was beneficial to the formation of needle like structure,while the increase of Mg component promoted the formation of irregular large particles.Finally,the activity,stability and anti-coking ability of Ni/Mg-Al-O catalysts（Mg/Al₂O₃ were set as 0/70,15/55,30/40 and 45/25,respectively）were evaluated.The results showed that all the four catalysts showed high catalytic activity,which increased the carbon gasification efficiency of 5wt%glucose from 24.6%to 73.0%at 500°C and the H₂ yield by three times;when Mg/Al₂O₃was set to 30/40,Ni/Mg-Al-O nano catalyst showed the best anti-coking ability.