| Resource lackage and environment problems have become a big challenge to our world in the 21st century. The application of biomass, which is an important sustainable resource, has attracted increasingly interests. Monosaccharides, which can be obtained from hydrolysis of biomass, can produce some important platform chemicals by acidic or basic catalysis, such as 5-hydroxymethylfurfural (5-HMF), levulinic acid (LA) and lactic acid. The traditional catalysts used in biomass conversion are homogeneous catalysts and some drawbacks are existed such as corrosion of equipment, separation problems and environmental unfriendly process. Therefore, development of solid acid/base is one of the ways to solve these problems. However, current studies on the application of solid acid/base are still insufficient:performances are still low; reaction mechanisms of the catalysts are seldom discussed. Thus, in this thesis, the performance of several typical solid acid/base catalysts such as zeolites and metal oxides for conversion of glucose to LA and lactic acid in hot compressed water were studied, as well as their reaction mechanisms.Firstly, structures and surface properties of the ZRP-5 zeolites have been characterized and their catalytic performance in glucose conversion has been examined. Compared to the non-catalyzed process, ZRP-5 zeolite can remarkably promote 5-HMF to form LA. And the SiO2/Al2O3 ratios of the zeolites have great effects on their perfromances. The highest yield of LA is obtained on the zeolite with SiO2/AlO3 ratio of 30. Moreover, both the pore structure and surface acidity have the influence on the conversion of glucose.Secondly, the forming ZRP-5 zeolite, which was formed by using Kaolin as support and Pseudo boehmite as binder, was examined on glucose conversion. It has been found that increasing amount of ZRP-5 zeolite may promote dehydration. Nevertheless the fragmentation is enhanced by increased pseudo boehmite. The optimized forming conditions were as following:the composition is 35 wt% ZRP-5 zeolite,30 wt% Kaolin and 35 wt%Pseudo boehmite; poresize is 178μm; solid content is 35 wt%; and calcination time is 2 hours. The highest yield of lactic acid obtained in our experiment is 47.7%. The reason for the high yield of lactic acid can attribute to the acid-base synergic effect of the hybrid catalyst.Thirdly, the single and binary mixed oxides that contain Al, Ti, Zr or Mg were prepared by coprecipitation method. The metal oxides can remarkably boost glucose conversion, and the surface acid/base amount and strength significantly influenced the distribution of main products. Solid solutions are formed in the mixed oxides. Compared to the single oxides, the mixed oxides improved little on the dehydration, but obviously improve the yield of lactic acid which comes from the fragmentation of glucose. The Mg-Al hydrotalcite, which contains large amount of strong acid/base sites and medium base site, gives the highest yield of lactic acid of 37 mol%. However, large amount of humins are also formed and the total organic carbon (TOC) amounts are lower than 40%. Moreover, some Mg ions are detected in the reacted solutions which indicate that leaching problem of Mg-Al hydrotalcite exists. On the other side, the binary mixed oxides with Ti, Al and Zr showed good stability in the reaction. Among these catalysts, Al-Zr mixed oxide has better yield of lactic acid up to 32.8%, and the TOC value is close to 70%, which gives the best application performance.Fourthly, influences of the Al/Zr composition, preparation method and calcination temperature on the structure, surface properties and catalytic performances of the Al-Zr mixed oxides were examined, respectively. Preparation method had little influence on the catalytic activity. The best calcination temperature is 500℃for the highest yield of lactic acid. The composition has a significantly influence on the structure and performance. When the amount of Al and Zr is close, a large amount of solid solutions are formed and increased the yield of lactic acid. The temperature programmed desorption (TPD) analysis results show that Al can increase the amounts of the strong and medium acid/base sites on the mixed oxides, whereas increasing Zr amount may strengthen the strength of the medium base sites. The medium base sites which CO2 desorption temperature is above 200℃are helpful for the lactic acid formation.Lastly, formation mechanism of lactic acid over Al-Zr mixed oxide was proposed by examination of reactions with different reactants:(1) the mixed oxide can accelerate the LB AE transformation of glucose to form 1,2-enol intermediate and fructose; (2) Existance of medium and strong base sites on the mixed oxide can promote the 1,2-enol intermediate and fructose to form C3 products including glyceraldehyde and dihydroxyacetone by double bond rules or retro-aldol condensation reactions; (3) Glyceraldehyde can easily form 1,2-enol intermediate and dihydroxyacetone through LBAE transformation, but the isomerization from dihydroxyacetone to glyceraldehyde is inhibited; (4) Glyceraldehyde or 1,2-enol is dehydrated to form pyruvaldehyde; (5) The medium and strong base sites on the Al-Zr mixed oxides enhance the benzilic rearrangement reaction of pyruvaldehyde to form lactic acid.
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