DEHYDRATION AND OXIDATIVE DEHYDROGENATION OF ETHANOL OVER ALUMINA CATALYST MODIFIED WITH SILVER-LITHIUM

Abstract

The research was aimed to investigate the characteristic and catalytic properties of mixed-phase alumina catalysts and Ag/Li modified mixed-phase alumina catalysts. In the first part, ethanol dehydration over mixed-phase alumina catalysts was investigated. The mixed gamma and chi phase alumina prepared by the solvothermal method of the mixed solution (toluene and 1-butanol) displays the attractive chemical and physical properties for the catalytic dehydration of ethanol to ethylene. The high acid site density apparently results in high catalytic activity for the mixed ɣ- and χ- alumina with 50 wt% of ɣ- and χ phases (CHI50). Moreover, the large amount of the adsorbed water on alumina surface can result in increased ethylene selectivity as observed by XPS analysis. In the second part, the influences of Ag/Li modification on mixed-phase alumina was investigated for oxidative dehydrogenation of ethanol to acetaldehyde. The result shows that high catalytic activity and acetaldehyde selectivity for Ag/Li modified the mixed ɣ- and χ- alumina with 50 wt% of ɣ- and χ phases (AgLi-CHI50) corresponded to the oxidation state and reduction behavior. In addition, in order to investigate surface-structure sensitive on silver catalyst, the adsorption of H2O onto the A and B type steps on an Ag single crystal by temperature programmed desorption was studied. A silver curved crystal represents a continuous range of surfaces structures ranging from [5(111)x(100)] via (111) to [5(111)x(110)]. LEED and STM studies verify that the curvature of sample results predominantly from monoatomic steps. For submonolayer of H2O coverage, a small and linear dependence of the desorption temperature on the A and B step density were observed