Hydrogen Production From Methanol Steam Reforming Over The Self-activated Cu₂O/ZnO Catalyst

As one of the most promising fuels of the twenty-first century,hydrogen faces safety concerns in both its manufacture and use.As a result,there is currently widespread support for the use of liquid fuels as a substitute.Methanol is a hydrogen-rich renewable fuel that can be obtained from biomass and other renewable sources in terms of liquid fuel.It has a high carbon-to-hydrogen ratio and no strong C-C bond.Methanol steam reforming（MSR）has a high selectivity for H2,a product with a low CO content,in all methanol hydrogen production processes.Copper-based catalysts typically have high activity and low cost when compared to VIII-X metal catalysts.However,the formation of coke and the sintering of copper active components are the major limitations for endothermic MSR.The goal of the research is to create copper-based catalysts with high reaction activity,selectivity,and stability.As a result,more research into the interface reaction mechanism of copper-based catalysis is required,as well as clarification of the relationship between interface properties and catalytic performance.The main work of this article are as follows:（1）A nanoscale Cu2O/ZnO catalyst with self-activating function,dual catalytic sites,and good high-temperature stability was designed.Based on RSM and BBD,a quadratic polynomial function was established to study the effects of temperature（T=450-550℃）,molar ratio of steam to carbon（SCMR=1.5–2.5 mol/mol）,and weight hourly space velocity(WHSV=4-6 h^-1)on H2 yield and potential H2 yield.Selecting an optimization scheme with a maximum expected value of 0.957 and using an ideal function to predict MSR,92.1%hydrogen yield and 97.2%potential hydrogen yield were obtained,respectively.Under the condition of 550°C,the selectivity of hydrogen is 99%within 36hours.The positive effect of the support ZnO on the sintering resistance of the catalytic active component copper was discovered using transmission electron microscopy and H2-TPR.（2）Self-activated nano Cu2O/ZnO catalysts with different Cu/Zn ratios were prepared under optimal catalytic conditions to accelerate the strong interaction between metal and supports.In the activation stage,different reducing agents（H2O/CH3OH/N2 and H2/N2）were used to control the catalytic surface reconstruction and optimization.The physical and chemical properties of copper and zinc active sites,as well as the quantitative changes caused by the migration and evolution of reducing carriers on the copper surface,were investigated.Cu XZn-R catalyst obtained 98.75%-99.71%hydrogen selectivity and very low CO selectivity（0.81%–5.10%）within 6 h.The hydrogen content remained stable between 72.93%and 74.77%.Self-activation was caused by the H2O/CH3OH/N2 mixture,which accelerated the migration of ZnO to the Cu surface and the formation of the highly active alloy Cu Zn.The carbon deposition in 72-hour MSR was eliminated by decorating the copper surface with strong metal-carrier interaction.（3）In MSR,the migration of ZnO and the subsequent Cu Zn alloying occur simultaneously.Due to induction and reduction effects,the Zn²⁺species in ZnOx were further reduced to Zn⁰,and the atomic images demonstrated the possibility of Cu Zn alloy formation.H2O/CH3OH/N2-induced activation leads to densification of the ZnO migration layer to a thickness of 30-50 nm,and particle size had no effect on the encapsulation of the activated catalyst.Methanol had a slightly lower reducibility than direct hydrogen reduction,resulting in the migration of a small amount of ZnO to the surface of Cu and its reduction.This change resulted in a nearly 30%improvement in catalytic performance.High zinc coverage could improve the catalytic activity,but it was not the most direct factor to control the catalytic activity,and the number of ZnO centers must be considered.H2O/CH3OH/N2 activation increased the abundance of Cu Zn alloy-ZnO sites,and the amount of ZnO on the copper surface had a direct effect on catalytic efficiency.The electron exchanges between Cu2O and ZnOX were enhanced by methanol activation.The analysis of in-situ time-resolved DRIFTS revealed that methanol-induced activation resulted in a more abundant Cu Zn-ZnO active interface.The DFT results confirmed that the Cu-Zn alloy-ZnO sites had a synergistic effect on*H2O dissociation and*CH3O dehydrogenation.