A series of palladium catalysts with ca. 1 wt% palladium supported on mesoporous silica with different pore sizes (MCM-41, SBA-15, and MCF) were prepared by deposition of colloidal Pd nanoparticles (Pd/X_col) and Pd(II)acetate solution (Pd/X_imp). MCM-41 and SBA-15 showed the XRD characteristic peaks indicating highly ordered hexagonal pore structure while MCF consisted of spherical cell and frame structure with average pore size of 2.7, 3.9, and 7.8 nm, respectively. Sizes of the colloidal Pd nanoparticles were about 2.3 nm. The supports pore structure did not affect the Pd particle size of Pd/X_col catalysts. For the Pd/X_imp, the Pd particle size was increased with increasing pore diameter of the supports. However, the largest Pd particle size was obtained on Pd/SBA-15_imp since the Pd particles were formed in a long cylindrical shape similar to SBA-15. The Pd/SBA-15_col exhibited the best catalyst performance in the liquid-phase selective hydrogenation of phenylacetylene under mild conditions (40 degress celsius, H2 pressure = 1-5 bar, 30 min). The appropriated pore structure and pore size of SBA-15 could provide a better encapsulation of Pd particles so that high styrene selectivity was attained at complete conversion of phenylacetylene. All the Pd/X_col catalysts exhibited no change in the catalyst activities/selectivity during the recyclability test for four cycles while the Pd/X_imp showed an increase of catalyst activity and lower styrene selectivity in some cases.

This thesis offers novel methods for catalyst and process design for the selective hydrogenation of acetylene and 1,3-butadiene. The author predicts the properties of supported Pd–Ni bimetallic catalysts using density functional theory (DFT) calculations and temperature-programmed desorption (TPD). The excellent correlation between model surfaces and supported catalysts demonstrates the feasibility of designing effective bimetallic catalysts for selective hydrogenation reactions. The author also proposes a method for designing non-precious metal catalysts to replace precious metals. She modifies the process of selective hydrogenation of acetylene by coupling the selective adsorption to the selective hydrogenation in the liquid phase, as a result of which the ethylene selectivity is greatly improved and heat transfer is greatly enhanced. Lastly, by analyzing the mechanism of liquid-phase hydrogenation, the author proposes a multi-stage slurry bed reactor for industrial applications.“/p>

The removal of trace amounts of acetylene in ethylene streams is a high-volume industrial process that must possess high selectivity of alkyne hydrogenation over hydrogenation of alkenes. Current technology uses metallic nanoparticles, typically palladium or platinum, for acetylene removal. However, problems arise due to the deactivation of the catalysts at high temperatures as well as low selectivities at high conversions. Pore expanded MCM-41 is synthesized via a two-step strategy in which MCM-41 was prepared via cetyltrimethylammonium bromide (CTMABr) followed by the hydrothermal treatment with N,N-dimethyldecylamine (DMDA). This material was washed with ethanol to remove DMDA, or calcined to remove both surfactants. PE-MCM-41 based materials were impregnated with palladium, gold, and palladium-gold nanoparticles. The removal of DMDA had an effect on both the conversion and selectivity, in which they were found to drop significantly. However, by using the bimetallic PdAu catalysts, higher selectivity could be achieved due to increased electron density.