Catalytic Performance of Micro-Mesoporous Zirconosilicates Prepared by Non-Hydrolytic Sol-Gel in Ethanol-To-Butadiene Transformation and Related Reactions

Synthesis of 1,3-butadiene (BD) from ethanol has experienced a true renaissance in recent years due to ecological and economic reasons. The open porosity and number of Lewis acid sites in metal silicates (M = Zr, Ta) have been reported in numerous studies as key factors enabling reaching high BD productivity. However, some microporous zeolites recently displayed very high BD productivity. To gain a deeper insight, we have applied non-hydrolytic sol-gel (NHSG) – a method well-known to produce highly porous and homogeneous metal silicates – in the preparation of zirconosilicates with varying micropore volume. The porosity (N2 adsorption-desorption experiments), structure (IR, XPS, NMR, and DRUV-Vis spectroscopy, XRD, MAS NMR), and acidity (IR spectroscopy combined with pyridine adsorption) of these materials have been described in detail and compared to a benchmark sample prepared by dry impregnation. Above mentioned characterization methods proved that NHSG preparation provided highly homogeneous Zr dispersion in silica leading to almost doubled Lewis acid site numbers and higher activity in ethanol-to-butadiene (ETB) transformation, Meerwein-Ponndorf-Verley (MPV) redox reaction, and aldol condensation, in comparison to the catalyst prepared by dry impregnation. The fraction of micropore volume in micro-mesoporous samples (ranging from 27 % to 69 %) did not play a significant role: The activity in all three catalytic reactions followed the acid site numbers. The selectivity and long-term stability in ETB process were similar for catalysts prepared by NHSG and dry impregnation.