Ruthenium (II) phosphine/mesoporous silica catalysts: The impact of active phase loading and active site density on catalytic activity in hydrogenation of phenylacetylene

Abstract

Ruthenium (II) supported catalysts containing various amounts of [(η 5-MeC 5H 4)Ru(η 3-PPh 2CHCH 2)(η 1-PPh 2CHCH 2)] + deposited on aluminated mesoporous silica of HMS type (Si/Al = 20 or 40) were synthesized by ion exchange method. The solids were characterized by XRD, 27Al MAS NMR, FTIR and UV–vis spectroscopies. The textural properties were determined from nitrogen adsorption at 77 K. Textural analysis showed that increased loading of ruthenium complex onto support with high density of exchange sites (high Al content) eventually leads to overcrowding of active species in pore sections close to the pore mouth and hinders access to sites located deeper within the pore network. All HMS supported catalysts proved active and selective in phenylacetylene semihydrogenation under mild conditions (temperature 40 °C and H 2 pressure of 1 atm), their performance showing a complex pattern depending on the catalyst loading with the active phase and the degree of support alumination. Results indicate that the optimum catalytic performance requires high number of active sites within the catalytically active zone near the pore entrance, simultaneously avoiding blockage of the pore system and loss of the site isolation effect (controlled by Si/Al ratio and active phase content). Best heterogenized catalysts are more active than unsupported ruthenium complex in the homogeneous system. The supported catalysts are stable under reaction conditions and can be easily recovered and reused, without any loss of catalytic activity and selectivity.