Synthesis, Characterization And Application Of Novel Catalysts For Selective Oxidation Of Alcohols And Methanol To Hydrogen Reactions

Catalysis is now playing a leading role in chemical industry. Research on catalysis has become a key technology, which is in almost every part of people's life and development of economy and society. It is playing an important part in saving energy, simplifying production procedures and protecting environment. It's been a significant subject of how to design effective new catalysts with the purpose of protecting environment and satisfying the requirement of atomic economy. In order to synthesize more effective catalysts, we can work on the present preparation methods or explore new synthesis techniques to develop functional materials with better performance in catalysis. Further, researchers can work on developing unique novel catalysts with special structures. Material science has offered us new thoughts and directions in designing effective advanced catalytic materials. It is significant for chemists to take advantage of research technologies and results of material science to develop various kinds of catalysts according to actual requirements in production based on mechanism and characteristics of catalytic reactions.It is a competitive process route of making carbonyl compounds, including aldehydes and ketones, from selective oxidation of alcohols. The target products are one basic kind of fine chemicals and organic intermediates. Gas phase oxidation of aliphatic alchohols has the advantages of zero use of solvent, easy separation of products and facile recovery of catalysts. Major present catalysts for gas phase oxidation of alcohols are silver-based catalysts, among which, bulk electrolytic silver catalyst is the most widely applied one. It is essential for electrolytic silver catalysts to work above 500℃to achieve satisfying performance. It is hard to present good selectivity at higher temperatures, while at lower temperatures it shows deficient catalytic activity for oxidation of alcohols. As for supported silver catalyst, its properties of low thermal conductivity and difficulty to recovery limit its industrial application. Especially, for various kinds of long chain alcohols, none of the present catalysts can show satisfying performance. Our work focuses on developping novel effective catalysts with new structure on foundations of mechanism of catalytic oxidation of alcohols from the point of view of catalyst design.The process of producing hydrogen from methanol is an important subject in research on fuel cell vehicles. The most applied catalysts are noble metal based catalysts and copper based catalysts. Noble-metal based catalysts have good activity under low temperatures but their limited resource and CO-poisoning features have limited their industrial application, while Cu-based catalysts suffer from poor thermal stability above 300℃due to the sintering of metals. Aiming at these problems, we work on preparing new bimetallic catalyst and noble metal-like catalysts adopting new fabricating techniques to develop effective methanol to hydrogen catalysts.In this work, our research concentrates on the following fields:1) the preparation of micro-dendritic silver catalyst via electroless metal deposition method and their application in alcohol oxidation with satisfying selectivity of the corresponding aldehydes; 2) the preparation of Ag@SiNW catalyst via electroless metal deposition method and their catalytic performance in oxidation of long chain alcohols; 3) the preparation of bimetallic Cu-Pt@SiNW catalyst via electroless metal deposition method and their catalytic application in methanol steam reforming reaction; 4) the preparation of nanoporous Mo2C NWs catalyst with organic-inorganic hybrid as the precursor and their performance compared with bulky Mo2C catalyst synthesized via TPR method in methanol decomposition; 5) the preparation of supported Mo2C catalyst and their performance in methanol decomposition.In mechanism research of alcohol oxidation reactions, it is found that (111) crystal plane of silver catalyst favers selective oxidation pathway of alcohols. Therefore, we conducted our research based on the present mechanism and fabricated novel micro-dendritic silver catalyst with selective orientation of (111) crystal plane via electroless metal deposition by making use of the spontaneous redox reaction between AgNO3 and Si with silicon wafer as the substrate. In preparation process, samples with different selective orientation degrees could be fabricated by regulating AgNO3 concentration in reaction solvent. These samples show distinguishing selectivity of 1-octanal in probe reaction of oxidation of 1-octanol. This result demonstrates the close association between catalytic selectivity of the objective product and selective orientation property of the as-prepared catalysts. When applied to oxidation of 1,2-proplyene glycol, micro-dendritic silver catalyst can effectively improve selectivity of methylglyoxal by reducing over-oxidation products. Moreover, micro-dendritic silver catalyst shows better performance than electrolytic silver catalyst in oxidation of both aliphatic primary alcohols and aliphatic diols.It has always been a hotspot and difficulty of fabricating silver-based catalysts with high dispersion degree and good stability for selective oxidation of alcohols. We designed novel silver catalyst with special morphology of silver particles embedded in silicon nanowire arrays combining the specialties of electrolytic silver and supported silver catalysts. Ag@SiNW catalyst is easily prepared by eletroless metal deposition method with cheap silicon powder as the substrate, followed by calcination process. The special structure of Ag@SiNW catalyst offers open microenvironment, which can effectively reduce diffusion limitation effect in catalytic reactions. Separate Silver particles embedded in silicon nanowire arrays have excellent anti-sintering property. When applied in selective oxidation of aliphatic primary alcohols, Ag@SiNW catalyst shows good catalytic activity and selectivity of corresponding aldehydes under lower temperatures.Bimetallic Cu-Pt catalyst with particles embedded in silicon nanowire arrays support (Cu-Pt@SiNW) is fabricated via eletroless metal deposition method with silicon powders as the substrate. When applied to steam reforming of methanol, it shows better catalytic stability and CO2 selectivity than one component Pt counterpart, while shows better hydrogen selectivity than one component Cu counterpart through interaction between Cu and Pt. Mo2C nanowires catalyst is synthesized with organic-inorganic hybrid as precursor. Its unique nanoporous one dimensional morphology provides larger specific area and better anti-sintering property than Mo2C catalyst prepared by TPR method. When applied to methanol decomposition reaction, it shows better catalytic stability and hydrogen production rate.Supported Mo2C catalyst fabricated with organic-inorganic hybrid as precursor is one easily-made and effective catalyst for producing hydrogen from methanol. The highest hydrogen production rate achieved in our experiment is as high as 3780μmol·min-1·gcat-1·Cobalt works as an important promoter for the as-prepared supported Mo2C catalyst. Co working as a CNT-formation catalyst effectively transforms carbon deposition on Mo2C nanoparticles and exposes the active sites. But the existence of Co also increases the by-product selectivity as a result of C-O bond scission of methoxy intermediate. Thus, only under appropriate Mo/Co molar ration, can best performance of Co-Mo2C/CNT catalyst be achieved.