Performance Of Palladium-based Catalysts For Direct Synthesis Of Hydrogen From Hydrogen And Oxygen By Doping

Hydrogen peroxide is a green and envir-onmentally fr-iendly chemical raw material.It has strong oxidizing properties and no pollution after use.Therefore,it is widely used in various fields.The synthesis methods of hydrogen peroxide,from early to the present anthraquinone method,commonly have the obvious disadvantages such as harsh reaction conditions,heavy equipment and large energy consumption.Therefore,people hope to find an economical and convenient green production method to replace traditional production technology.Recently,direct synthesis method has attracted widespread attention because of its simple reaction conditions and raw material(hydrogen and oxygen).However,it still has severalproblems such as the safety of reaction,productivity of catalytic synthesis,and low conversion efficiency.In this paper,the catalytic activity of the catalysts in the direct synthesis of hydrogen peroxide from hydrogen and oxygen were studied by doping palladium-based catalysts with different metals and halogens.This provides a promising strategy for the development of highly active and selective catalysts for the direct synthesis of H2O2.The main research contents are as follows:(1)According to the simulation calculation,it is predicted that the PdW catalyst can exhibit excellent catalytic performance.Therefore,this paper adopts the industrial impregnation method without adding any additives,using C,MgO,SiO2,Ti02,CeO2,Al2O3 as the carrier,adding non-noble metal W to synthesize PdW bimetallic catalysts.Characterization results demonstrate that the metal particles are anchoredon the support surface.In the performance tests,W-Pd/MgO shows good performance in both the main reaction and the side reaction catalytic ability.W-Pd/Al2O3 only has outstanding catalytic activity in the synthesis of the main reaction H2O2.This is because Al2O3 and WO3 acids could efficiently catalyze H2 and O2 to H2O2 in the reaction,and then inhibit further reaction of the product.(2)Using the alumina as a carrier,changing the metal loading ratio to explore the optimal composite material formed by W doping into a palladium-based catalyst.The experiment proves that the W-Pd/Al2O3 catalyst with "core-shell" structure is synthesized.When Pd/W is 4:1(total metal loading is 5 wt%),the productivity and selectivity of H2O2 in the direct synthesis of H2O2 can reach 156.9 molH2O2kgcat-1h-1 and 64.5%,respectively.It is worth mentioning that the utilization rate of the new composite catalyst in the cycle stability experiment is higher than 80%,and it can be used five times without showing reduced catalytic efficiency.(3)Pre-halogenated palladium-based catalysts were used to study the effect of halogen-modified on the performance of palladium-based catalysts for the direct synthesis of hydrogen peroxide from hydrogen and oxygen,which was compared with the method of adding halide to the reaction solution directly.The experiment found that Br-and Cl-are catalyst additives,and the addition of F-and I-is not conducive to the synthesis of H2O2.Among them,the halogen-modification catalysts can obtain better catalytic effect,and exhibit more excellent catalytic activity in the the direct synthesis of hydrogen peroxide from hydrogen and oxygen.