The Role of Brønsted and Lewis Acid Sites in Acetalization of Glycerol over Modified Mesoporous Cellular Foams

Abstract

The main objective of this work is to determine which kind of acidic sites, Brønsted (BAS) or Lewis (LAS), are more active and stable in the glycerol acetalization to solketal by means of Raman-monitoring. For this purpose, the mesoporous cellular foams (MCFs) were modified to obtain materials containing exclusively BAS occurring in different number and strength (samples MP-MCF (MP = (3mercaptopropyl)trimethoxysilane) and CS-MCF (CS = 2-(4chlorosulfonylphenyl)ethyltrimethoxysilane)) or the material containing exclusively LAS (NbMCF). Moreover, the materials containing both types of centers in different ratios (MoMCF and TaMCF) were also studied. Real-time Raman monitoring of the catalytic reaction allowed us to observe not only changes in substrates concentration and product yield but also the transformation of acetone−glycerol adduct (O•••CO vibrations) formed in the presence of a catalyst. The activity of the catalysts containing BAS depends on the number and strength of these centers, and the best performance was observed for CS-MCF. The maximum of solketal yield and the equilibrium state were achieved after 2 min from the start of the Raman monitoring. NbMCF containing exclusively LAS exhibited both the lowest conversion of glycerol and stability. The role of different recycling treatments was probed.

Brønsted Acid Ionic Liquids (BAILs) as Efficient and Recyclable Catalysts in the Conversion of Glycerol to Solketal at Room Temperature

“…The Raman bands of glycerol were rather weak in this spectral window, being located near 680 cm −1 . The most informative bands were those at 638 and 648 cm −1 , corresponding both to solketal, and that near 730 cm −1 associated to the formation of a glycerol and acetone adduct formed before cyclization into solketal, as pointed out recently by Stawicka and co‐workers . The formation of the intermediate was apparent from the first few minutes and its evolution depended strongly on the catalytic system.…”

Continuous-Flow Monolithic Silica Microreactors with Arenesulphonic Acid Groups: Structure–Catalytic Activity Relationships

“…The data in Table 1 confirmed that strength of BAS is comparable for all the samples. The value of A 200 /A 150 nearly close to unity is characteristic of strong acid sites [30,31]. The relationship between the pressure drop and the flow rate is of practical significance, providing additional knowledge which is useful in assessing process economics.…”

“…The data in Table 1 confirmed that strength of BAS is comparable for all the samples. The value of A200/A150 nearly close to unity is characteristic of strong acid sites [30,31]. The identification of acid sites and their strength were studied using pyridine (Py) adsorption combined with Fourier transform infrared (FTIR) studies.…”

Sulphated Zirconia Supported on Cordierite Honeycomb Monolith for Effective Synthesis of Solketal from Acetalisation of Glycerol with Acetone

“…1PDSABEA sample showed 100% selectivity, but modification of the BEA catalysts to be trickier, due to controlled dealumination. Different metal loaded catalysts showed decrease in their activity after 3–4 recycles with relatively poor selectivity due to leaching. BEA sample, also showed deactivation for the acetone due to high reactivity after several usage cycles.…”