The Pd/SiO2 catalysts for hydrogenation of D-glucose

Abstract

In this study, the effect of physical and chemical treatment on catalyst preparation was investigated, and also the activity of prepared catalysts was evaluated by hydrogenation of D-glucose. As a representative noble metal catalyst, palladium required to be distributed on a supports because it has high cost, finite resources, and sintering at high temperature. Since the dispersion and the particle size of palladium affect the catalytic activity, palladium catalysts with high metal dispersion were prepared through physical and chemical modification of the support properties. And the effect of palladium dispersion on hydrogenation of D-glucose was confirmed 1) Ordered mesoporous silica (OMS) with uniform pore structure was prepared and the effect of the pore structure on the palladium dispersion was investigated. In general, a material having a high specific surface area is suitable for support of catalyst. However, the catalysts using OMSs have relatively low palladium dispersion of less than 6% although it has a high specific surface area of 500 m2 / g or more. It is reason that silica has a low metal-support interaction and especially, OMSs with uniform pore structure have higher surface stability. So that palladium particles cannot be uniformly distributed on silica, and be supported on OMSs with severely aggregated to each other 2) The silanol group (-OH), which is one of the functional groups of SiO2, interferes with the reduction of palladium because it strongly bonds with palladium ions (–PdO) during the preparation of the catalyst. In this study, the silanol group was removed through the thermal and the ammonia treatment of SiO2, and the catalysts were prepared with pretreated SiO2. As a result, it was confirmed that the silanol group on the SiO2 surface was completely removed by calcination above 700 ° C and ammonia treatment above 200 ° C. The Pd / SiO2_700 and Pd / SiO2_A200 catalysts which the silanol groups were removed had a high palladium dispersion of 13.02% and 8.82%, respectively, which were about 3-4 times higher than those of the catalysts without surface modification. Therefore, it was confirmed that the removal of the silanol group positively affects the increase of the dispersion of palladium. 3) The catalytic activity test was conducted by hydrogenation of D-glucose. Hydrogenation was carried out using the prepared catalysts with different metal dispersion, and the effect of palladium dispersion on catalytic activity was confirmed. Experimental results show that the hydrogenation with Pd/SiO2_700 with the highest dispersion (13.02%) had much higher sorbitol yield of 65.10% compared to Pd / SiO2_N with low palladium dispersion (2.81%). It was confirmed that as the palladium particles are evenly distributed, the number of effective collisions between the reactant and the catalytic active sites increases, so that the catalyst activity increases with the use of the highly dispersed catalyst.