Solvent Influence on the Catalytic Activity and Surface Polarity of Inorganic Solid Acids

Abstract

The surface-mediated hydride-transfer reaction of 1,4-cyclohexadiene with triphenylmethylium induced by two silicas, an alumina, and an aluminosilicate as solid acid catalyst, respectively, has been kinetically studied as a function of the polarity of the surrounding solvent. The specific rate constants k′ have been determined in 10 different solvents. Generally, k′ decreases with increasing polarity of the solvent. Kamlet-Taft's R (hydrogen-bond acidity) and π* (dipolarity/polarizability) parameters of the solid acid/solvent interface have been determined for alumina and aluminosilicate in various solvents. Fe(phen) 2 (CN) 2 [cis-dicyanobis(1,10phenanthroline)iron(II), ( 1)] and Michler's ketone [4,4′-bis(N,N-dimethylamino)benzophenone, (2)] were used as solvatochromic surface polarity indicators. The UV/vis spectra of the two surface polarity indicators 1 and 2 adsorbed on solid acid catalysts from the solvents were measured by the reflection mode and the UV/vis absorption maxima were used to calculate the R and π* values of the catalysts. R of the solid acid catalyst/ solvent interface decreases with increasing β term (hydrogen-bond accepting) ability of the solvent, whereas the π* term of the solvent marginally modifies the interfacial polarity. k′ increases for each individual solvent with increasing β of the catalyst solvent interface in the order series silica < alumina < aluminosilicate. It can be shown that R of the solid acid catalyst/solvent interface decreases with increasing β term (hydrogenbond accepting) ability of the solvent, whereas the π* term of the solvent marginally modifies the interfacial polarity.

Propene carbonate intensified cyclohexane oxidation over Au/SiO2 catalyst

“…Generally, the catalytic performance strongly depends on the nature of the reaction media, such as polarity, and molecule volume [18][19][20]. In particular, the increase in solvent polarity can stabilize the reaction intermediate states due to the enhanced intermolecular forces between the solute and solvent during solvation, and thus facilitate the reaction process.…”

Quantifying Surface Properties of Silica Particles by Combining Hansen Parameters and Reichardt's Dye Indicator Data

“…For liquids, another method to determine polarity exists, namely, the employment of solvatochromic indicators . The working principle is as follows: The indicator, usually a dye, changes its color depending on the polarity of its immediate molecular environment.…”

“…For liquids, another method to determine polarity exists, namely, the employment of solvatochromic indicators. [61][62][63][64] The working principle is as follows: The indicator, usually a dye, changes its color depending on the polarity of its immediate molecular environment. The solvatochromic effect, which is for some dyes still in the focus of nowadays research, [65,66] can occur in two different ways, either as negative solvatochromism where a hypsochromic shift (blue shift) can be observed with increasing polarity, or as positive solvatochromism with a bathochromic shift (red shift).…”

Solvent Effect Inside the Nanocage of Zeolite Catalysts: A Combined Solid-State NMR Approach and Multiscale Simulation

“…Cerveny et al 13 reported that the solvent had a significant influence on the selectivity for perillyl alcohol by the combination of Sn-MCM-41 and DMSO solvents. Spange et al 14 investigated the surface-mediated hydride-transfer reaction on different inorganic solid acid catalyst with various solvents, and it was found that the rate constants decreased with the polarity of solvent increasing. Roeffaers et al 15 recently reported that the pore selectivity of H-ZSM-5 zeolites was promoted by changing the solvent polarity.…”