Screening, Support Effect And Fundamental Studies Of Catalysts For Glycerol Hydrogenolysis

As the main by-product of biodiesel preparation derived from vegetable oil, glycerol has become more and more excessive in the past decade. Therefore, the catalytic conversion of glycerol to value-added chemicals attracted much attention recently, among which catalytic hydrogenolysis of glycerol to propanediol is one of the most promising routes. At present, catalysts utilized in glycerol hydrogenolysis focused mainly on metal ruthedium and copper, but the low selectivity of Ru-based catalysts or poor glycerol conversion of Cu-based ones limit their intensive application. The rational design of high performance catalysts is still the most critical point for glycerol hydrogenolysis process. In this thesis, we aimed to systematically screen the active metals and supports of catalysts used in glycerol hydrogenolysis, and also investigate the relationship between the microstructure, chemical adsorption behavior and catalytic properties of the optimized metal-oxide catalysts, which are believed to be helpful for rational design of high performance catalysts.The main work was summarized as follows:(1) The screening of the carbon supported catalysts for glycerol hydrogenolysis was carried on. By correlating the C-C and C-O bond cleavage ability of the carbon supported noble metals with their catalytic performance, palladium is chosen to be the suitable active metal for further study due to its good activity and1,2-PD selectivity.(2) The screening of supports for palladium based catalysts was conducted systematically. Palldium supported on different oxides, namely inert CeO2, Al2O3, ZrO2, ZnO and reducible Fe2O3, Co3O4, NiO, were synthesized using co-precipitaion method. The obtained catalysts were characterized by XRD, H2-TPR, CO(CO2)-TPD, TEM technology and tested in glycerol hydrogenolysis reaction. The reuslts revealed that the strong metal-support interaction (SMSI) between palladium and support played vital role to glycerol conversion and1,2-PD selectivity in hydrogenolysis. Pd/iron oxide catalyst showed the best catalytic performance among these catalysts, which could be contributed to the formation of sub-nanoscale Pd-Fe alloy clusters on its surface. In addition, effects of various parameters such as reaction temperature and pressure were investigated to optimize the catalytic performance of Pd/iron oxide catalyst. Further study showed that the catalyst was almost stable and recyclable for glycerol hydrogenolysis reaction.(3) The support morphology effect on the catalytic performance of Pd/iron oxide in glycerol hydrogenolysis was investigated. Rod-like and plate-like iron oxides were synthesized using surfactant-free method. The different surface property, SMSI and chemisorption behavior for both iron oxides were studied. The dominated facet for plate-like and rod-like iron oxide demonstrated by HRTEM and XRD were (001) and (110), respectively. The both iron oxides supported Pd catalysts were used as model catalysts for glycerol hydrogenolysis. The catalytic results showed that the glycerol conversion of Pd/plate-like iron oxide was much higher than that of Pd/rod-like iron oxide. The reason should be due to the higher oxygen density of the exposed polar (001) surface of plate-like iron oxide, which was beneficial to the glycerol conversion by enhancing the SMSI effect and surface basicity of the catalysts.(4) A simple one-pot method for preparation of Pd/iron oxide nano-catalyst was developed. By varying the preparation conditions, such as concentration, temperature and heating rate, the size of obtained Pd/iron oxide composite nano-catalysts could be tailored, which exhibited good catalytic activity in glycerol hydrogenolysis reaction.(5) The effect of mixed oxide support on Pd/iron oxide catalyst was studied. To improve catalytic performance in glycerol hydrogenolysis reaction, another metal oxide was introduced in Pd/iron oxide catalyst according to the basic catalytic mechanism. The results showed that too strong basicity obtained by the addition of MgO accelerated the glycerol conversion but was greatly harmful to the1,2-PD selectivity. By screening several basic oxides, ZnO was proved to be beneficial to both glycerol conversion and1,2-PD selectivity when added in the Pd/iron oxide catalyst. Furthermore, a Pd/Fe90Zn10Ox catalyst could be obtained as a good choice for glycerol hydrogenolysis by optimization of zinc oxide content in catalyst.