The Composite Oxide Catalysts For Hydrogen Production By Methanol Steam Reforming Catalyst

In recent years,the development of oil alternatives as fossil fuel substitutes has become an important choice to meet the needs for the continuous growth of the global population and the shortage of oil resources.Among many new energy sources,hydrogen,as a clean and efficient energy source,is not easily compressed and liquefied due to its low boiling point,which limits its extensive application as a mobile energy source.However,methanol is characterized by sufficient capacity,high hydrogen to carbon ratio,high energy density,easy storage,and convenient transportation in liquid form at room temperature,so it is very suitable for mobile hydrogen production.Hydrogen production by methanol steam reforming?MSR?has the advantages of highest hydrogen production efficiency,less by-products and mild reaction conditions.This paper focused on the activity of ZnO,Ce O₂ and Zr O₂ composite oxides in the hydrogen production by methanol vapor,and studied the role of ZnO,Ce O₂ and Zr O₂ in the whole catalytic system.In order to study the interaction between different metal oxides and their effects on catalytic performance,Zn Ce Zr O_x composite oxide catalysts with different molar ratios were prepared by hard template method.Through online testing of catalysts,the optimal catalyst is determined from the results of catalytic activity.The effect of different reaction parameters such as water-carbon ratio and air velocity on the selectivity and activity of the product in the reaction system of methanol steam reforming to produce hydrogen was investigated.The effects of ZnO content on the performance of Zn_yCe₁Zr₉O_x catalysts were studied for hydrogen production of methanol steam reforming?MSR?.The best-performing Zn₁Ce₁Zr₉O_xcatalyst exhibited full methanol conversion and higher H₂ production rate of0.31 mol·h^-1·g^-1_cat at 400°C.Characterization results based on XRD,BET,H₂-TPR,Raman,FT-IR,UV-Vis,XPS and CH₃OH-TPD revealed the synergistic effect among ZnO,Ce O₂ and Zr O₂ after forming a solid solution.The incorporation of Zn²⁺into Ce₁Zr₉O_xmatrix was found not only to modulate the ratio of surface O_Latt/O_Ads,but to also generate new Zn-O-Zr structure corresponding to the lattice/bridge oxygen to increase the selectivity of CO₂.The excess oxygen vacancies on the samples surface favor the decomposition of methanol to generate the undesired CO.This study proposes a new design strategy for developing highly efficient composite MSR catalysts by control of the lattice/bridge oxygen and surface oxygen vacancy.For Zn₁Ce_nZr_yO_x?n+y=10?composite oxide catalysts with different molar ratios,as the molar ratio of cerium and zirconium increases,the catalyst activity sequence at the reaction temperature of 400°C is Zn₁Ce₁Zr₉O_x>Zn₁Ce₂Zr₈O_x>Zn₁Ce₃Zr₇O_x>Zn₁Ce₄Zr₆O_x>Zn₁Z_rO_x>Zn₁Ce₆Zr₄O_x.Therefore,when the cerium-zirconium molar ratio is 1:9,the Zn₁Ce₁Zr₉O_x catalyst has the highest methanol conversion rate and hydrogen generation rate,and lower selectivity of carbon monoxide and dimethyl ether.In addition,when the space velocity was 5151 h^-1,the methanol conversion of the Zn₁Ce₁Zr₉O_x catalyst reached the maximum,indicating that the catalyst utilization rate was the largest.The selectivity of the intermediate dimethyl ether is the lowest,and the selectivity of carbon monoxide is the lowest,indicating that the space velocity of 5151 h^-1 is more conducive to the progress of the methanol steam reforming hydrogen production reaction.The molar ratio of steam to carbon?S/C?also has a great effect on the conversion of methanol and product selectivity.Although the increase in water vapor partial pressure will inhibit the decomposition of methanol,due to the further reaction of dimethyl ether as an intermediate product,it also promotes the decomposition of methanol.Therefore,when the water-to-carbon ratio is 1.4,it is more favorable for the hydrogen production via the methanol steam reforming.