Gas-phase hydrogenation of o-xylene over Pt/knitted silica-fiber catalysts

A knitted silica fiber was prepared and employed as a support material for platinum catalysts. Different knitted silica-fiber supported platinum catalysts were prepared using several platinum precursors. The catalysts were characterized by N₂ physisorption, H₂ adsorption, NH₃/H₂/o-xylene temperature-programmed desorption, scanning electron microscopy-energy-dispersive X-ray analysis, and X-ray photoelectron microscopy. Catalyst activity was investigated in the gas-phase hydrogenation of o-xylene at 360-460 K with o-xylene and hydrogen partial pressures of 0.06 and 0.36-0.73 bar. High o-xylene conversions (up to 99%) to cis- and trans-1,2-dimethylcyclohexane were achieved. The specific surface area and pore volume of the support and the platinum precursor affected the catalyst performance. A catalyst prepared from platinum nitrate with a metal loading of 5 wt % exhibited the highest hydrogenation activity. A maximum in hydrogenation activity vs temperature was observed, which was caused by decreased surface o-xylene coverage with a temperature increase. Residual surface chlorine was found to affect both the catalyst activity and the product stereoselectivity. The selectivity toward the formation of trans-1,2-dimethylcyclohexane is increased at higher operation temperatures.