Mchanism Study On Hydrogen Production By Sorption-Enhanced Methanol Steam Reforming Based On The Ga-modified Cu-MgO Catalytic Sorbent

Hydrogen energy has been irreplacable in the sustainable development of energy in the future due to its advantages such as high energy density,environmental friendness,flexible utilization forms,and wide applications.However,the difficult storage and transportation of hydrogen has greatly limited its industrial development.The in-situ generation of high concentration hydrogen can be achieved by the sorption-enhanced steam reforming of biorenewable methanol,and the problems of hydrogen production,storage and transportation can also be solved integrated.Nevertheless,this process also suffers from the poor reaction activity,and easy sintering and agglomerate of Cu based catalyst and CO₂sorbent.The in-depth exploration of the physicochemical properties and reaction mechanism of the Cu-based catalyst and Mg O-based sorbent is conducive to guiding the materials and to obtaining the ideal adsorption-enhanced methanol steam reforming hydrogen production performance.A series of Cu-Mg O-Ga₂O₃ catalytic sorbents were prepared via a sol-gel method for the adsorption-enhanced methanol reforming process,and the effect of the doping amount of Ga on the physical and chemical properties of the catalytic adsorbents.The experimental results show that the doping of an appropriate amount of Ga is beneficial to increase the specific surface area of the material,improve the pore size characteristics,and promote the uniform dispersion of the active phase Cu and Mg O adsorbents.Furthermore,the doping of Ga can induce the ions substitution in the material system,create more active sites over material surface,and thus improve the catalytic and the CO₂ adsorption performance.The prepared sample can achieve 100%high-concentration hydrogen production at 200℃,no CO is detected in the adsorption enhancement stage,and the material has good stability within 20 cycles.Combining with the in situ Diffuse Reflectance Fourier Transform Infrared Spectroscopy（in situ DRIFTS）and DFT calculations,the effect of Ga doping on the types of intermediates and the reaction pathway during the sorption-enhanced reforming process were investigated,which could guide the optimal design of materials and the selective regulation of products.The experimental results show that the doping of Ga is conducive to promoting the activation of water over the surface of the catalytic adsorbent and the contact of C-containing intermediate species with oxygen source species（O^*,OH^*）,and thus promoting the effective conversion of methanol.In addition,the doping of Ga can adjust the surface CO₂ adsorption carbonate type to lower the minimum CO₂desorption temperature and alleviate the sintering and agglomeration of the catalytic sorbent.The thermogravimetric experiment（TGA）and the double-exponential model were used to investigate the kinetics of CO₂ adsorption reaction of catalytic adsorbents under different Ga doping amounts and reaction temperatures.The results show that,due to the its stronger basicity and better pore size characteristics,the CO₂ adsorption reaction of Ga doped sample is always stronger than the un-doped one in the investigated temperature range,and the surface CO₂ adsorption reaction activation energy of the doped one is less affected by temperature.In this paper,the Ga-Cu-Mg O composite catalytic sorbents were prepared,the effect of Ga doping on the physicochemical properties and hydrogen production performance was investigated systematically,and the reation conditions were optimized,aming to provide a new idea for the catalytic-adsorption composite material and the efficient conversion of methanol to hydrogen production.