Studies On Hydrogen Production From Formic Acid, Methanol And Glucose By Homogeneous Catalysts At Low Temperatures

The depletion of fossil fuel reserves and the environmental pollution have become worldwide problems,so it is imminent to develop large-scale alternatives to fossil fuels nowadays.Because of the high energy efficiency and clean combustion characteristics,the renewable hydrogen is not only one of the most important chemicals in the chemical industry but also an important fuel of internal combustion engines and fuel cells in the future.Asa kind of low-carbon energy,hydrogen is regarded as the most promising clean energy in the 21stcentury.How to produce hydrogen safely,efficiently,cheaply and conveniently has become a key problem for the development of hydrogen energy.Organic small molecules such as methanol,formic acid and glucose are promising hydrogen storage materials because of its high hydrogen content,wide source,low cost and so on.However,the low reactivity and the relatively high content of CO at low temperatures in these dehydrogenation reactionslimit their practical application.To solve these problems,this paper will discuss and contrast a series of homogeneous organic complex catalysts.Catalysts with application potential were screened out and their kinetic and thermodynamic properties were further studied.In this thesis,the main results are divided into three parts as following:First,for HCOOH dehydrogenation at low temperatures,the mononuclear iridium catalyst and hetero-nuclear iridium-rhodium catalyst were firstly synthesized.By changing the experimental conditions,we found that different reaction atmosphere had a great influence on the reaction activity.When there?s trace oxygen in the reaction system,the activities of the two catalytic reaction systems were greatly improved by 18and 12 times,respectively.By controlling the oxygen content in the reaction systems,we explored the mechanism of the catalytic reaction.The oxygen and hydrogen could react with each other to directly generate hydrogen peroxide?H₂O₂?under the participation of the catalyst.Hydrogen peroxide may be the one directly participating into the activation process and caused the dramatic changes of chemical structures of the catalysts.The addition of hydrogen peroxide directly into the reaction system validated our conjecture.Second,for CH₃OH reforming dehydrogenation,a homogeneous catalyst[Cp*Rh?NH₃??H₂O?₂]³⁺were synthesized for the clean conversion of methanol and water into hydrogen and carbon dioxide.Hydrogen generation was observed with excellent turnover frequencies(TOF=83.2 h^-1)by[Cp*Rh?NH₃??H₂O?₂]³⁺at 70?without any addition of alkaline or organic materials.With the existence of homogeneous rhodium catalyst,no CO could be detected in the reforming gas.Comparison of several different catalysts revealed that the coordinative H₂O ligand is labile,and the left vacant site allows the metal center for catalysis,which finally accelerates the reaction rate.Third,for glucosedehydrogenationat low temperatures,comparative analysis of catalytic activities of various catalysts for hydrogen production from glucose under mild conditions were proceeded.The water-soluble ruthenium-based p-cymene pincer complex[?p-cymene?Ru?NH₃?]Cl₂ showed the highest activity and stability.No additional organic matter is required,renewable hydrogen with low CO concentration can be produced at 98?and constant pressure with a remarkable TOF value of 719h^-1.The formate formation was observed in the ¹H-NMR of the reaction solution at different reaction times.The mechanism of the homogeneous dehydrogenation of glucose was proposed and discussed.