Zhengfeng Shao

A Facile and Controlled Route to Prepare an Eggshell Pd Catalyst for Selective Hydrogenation of Phenylacetylene

Selective hydrogenation of phenylacetylene to styrene is an important industrial process in polystyrene production, because the polymerization catalysts are extremely sensitive to trace phenylacetylene in styrene feedstocks. Many efforts have been devoted to develop effective catalysts with satisfactory activity and selectivity to styrene. Supported Pd catalysts have been shown to be promising along these lines, although the catalysts must be modified by other transition metals to avoid complete hydrogenation of phenylacetylene to ethylbenzene. In the present case, we have tested the hypothesis that ethylbenzene formation can be suppressed by distributing active metals on the external surface of the support in the eggshell configuration. Many researchers have reported that eggshell catalysts are superior to uniform ones in some reactions, involving heat/ mass-transfer limitations. Iglesia et al. proposed a route to synthesize eggshell catalysts that involved support impregnation with a high viscosity liquid. In contrast, Ding et al. prepared Co/SiO2 catalysts with different distributions by reducing the capillary pressure. Other methods have also been developed, including spray method, metal organic chemical vapor deposition, and using porous hollow silica support. Unfortunately, several factors have limited the implementation of eggshell catalysts, including the long preparation period, high solvent cost, and difficulty in controlling the eggshell thickness. The controlled synthesis of the well-defined eggshell catalysts therefore still remains an important challenge. A facile and controlled route to synthesize the eggshell Pd/SiO2–Al2O3 catalysts is presented. The novel method involves CO reduction deposition of PdCl2 on SiO2–Al2O3 support at room temperature in ethanol aqueous solution. The as-prepared eggshell Pd catalyst exhibited a higher activity for converting phenylacetylene to styrene than a uniform one prepared by traditional incipient wetness impregnation. When the SiO2–Al2O3 support is added to the PdCl2-ethanol aqueous solution, a certain amount of palladium ions adsorb onto the oxide surface. After exposure to CO, the process of reduction can be expressed by the following [Equation (1)]:

Hydrogenation of succinic acid over supported rhenium catalysts prepared by the microwave-assisted thermolytic method

A series of metallic Re/C catalysts were prepared with the microwave-assisted thermolytic method by using decacarbonyldirhenium [Re2(CO)10] as a precursor for the hydrogenation of succinic acid. The results of FT-IR, UV-Vis, XRD, HRTEM, ICP, TPR and CO chemical adsorption showed that the as-prepared catalysts had well-dispersed rhenium nanoparticles on activated carbon. Changing irradiation time or rhenium loadings could effectively adjust the properties of Re/C catalysts which exhibited good catalytic performance for the hydrogenation of succinic acid. There were plenty of active sites on Re/C catalysts for the high concentration hydrogenation of succinic acid, and increasing temperature or pressure improved catalytic activity at a defined scope. From the kinetic study of succinic acid catalytic hydrogenation, there was a certain converting relationship between the different intermediates and the product distribution which could be controlled by variation of reaction time.

Creation of surface defects on carbon nanofibers by steam treatment

Abstract A direct strategy for the creation of defects on carbon nanofibers (CNFs) has been developed by steam treatment. Nitrogen physisorption, XRD, Raman spectra, SEM and TEM analyses proved the existence of the new defects on CNFs. BET surface area of CNFs after steam treatment was enhanced from 20 to 378 m 2 /g. Pd catalysts supported on CNFs were also prepared by colloidal deposition method. The different activity of Pd/CNFs catalysts in the partial hydrogenation of phenylacetylene further demonstrated the diverse surfaces of CNFs could be formed by steam treatment.

A novel approach to synthesize highly selective nickel silicide catalysts for phenylacetylene semihydrogenation

Abstract Nickel silicides (NiSi x ) have been prepared by carbon template for nanostructured NiO and further silicidization with SiH 4 /H 2 at relatively low temperature and atmospheric pressure. The results showed that the formation of nickel silicides involves the following sequence, Ni (cubic) → Ni 2 Si (orthorhombic) → NiSi (orthorhombic) → NiSi 2 (cubic), with increasing temperatures. The as-prepared nickel silicides showed above 92% selectivity to styrene in the semihydrogenation of phenylacetylene due to the electronic and geometrical effects derived from the addition of Si into Ni particles.