One‐Step Room‐Temperature Synthesis of [Al]MCM‐41 Materials for the Catalytic Conversion of Phenylglyoxal to Ethylmandelate

Abstract

Mesoporous [Al]MCM‐41 materials with nSi/nAl ratios of 15 to 50 suitable for the direct catalytic conversion of phenylglyoxal to ethylmandelate have been successfully synthesized at room temperature within 1 h. The surface areas and pore sizes of the obtained [Al]MCM‐41 materials are in the ranges of 1005–1246 m2 g−1 and 3.44–3.99 nm, respectively, for the different nSi/nAl ratios. For all [Al]MCM‐41 catalysts, most of the Al species were tetrahedrally coordinated with Si in the next coordination sphere of atoms. 1H and 13C magic‐angle spinning NMR spectroscopic investigations indicated that the acid strength of the SiOH groups on these [Al]MCM‐41 catalysts and the density of these surface sites are enhanced with increasing Al content in the synthesis gels. These surface sites with enhanced acid strength were found to be catalytically active sites for phenylglyoxal conversion. The [Al]MCM‐41 material with nSi/nAl=15 showed the highest phenylglyoxal conversion (93.4 %) and selectivity to ethylmandelate (96.9 %), whereas the [Al]MCM‐41 material with nSi/nAl=50 reached the highest turnover frequency (TOF=99.3 h−1). This is a much better catalytic performance than that of a dealuminated zeolite Y (TOF=1.7 h−1) used as a reference catalyst, which is explained by lower reactant transport limitations in mesoporous materials than that in the microporous zeolite.

NMR Spectroscopic Characterization of Flame‐Made Amorphous Silica‐Alumina for Cyclohexanol and Glyceraldehyde Conversion

“…Since SAx possess both lower acidity and surface areas compared to the De−Al‐HY zeolite, the excellent activity of the non‐porous SAx catalysts is attributed to the high external diffusion rates of reactant and product compared to the constrained internal diffusion occurring in the cages and narrow channels of zeolites. The absence of pore diffusion limitations in the SAx catalysts facilitates high TOFs similar to those reported earlier …”

Brønsted acid sites based on penta-coordinated aluminum species

“…Experiments using probe molecules have confirmed the role of flexible or PBS Si-OH···Al IV coordination as BAS in ASA569162021. Similar methods using ammonia probe molecules were applied here to demonstrate the acidity of the Si-OH···Al V coordination observed in dehydrated SA/10 and SA/50 (ref.…”

“…However, previous works have shown that the Al atoms with neighbouring SiOH groups (Fig. 1b,c) do not produce such a shift of the 1 H MAS signal of these groups569162021. Supplementary Fig.…”

“…Replacing Si atoms by more Al IV species can enhance the density of BASs, but it reduces the mean electronegativity of the framework, which thus leads to a decrease of the overall acid strength of BASs1819. Similarly, Al IV species incorporated into the amorphous silica network are able to generate BASs on ASA92021. The proximity between Al IV and silanol sites in ASA has recently been observed by nuclear magnetic resonance (NMR) correlation experiments between 29 Si and 27 Al nuclei, the sensitivity of which was enhanced by dynamic nuclear polarization22.…”

Palladium‐Catalyzed O‐Arylation Reaction Using Different Heterogeneous Catalyst Systems: The Role of Support

“…These two kinds of supports have amazing feature. Mesoporous materials like MCM‐41 and SBA‐16 have specific properties such as large BET surface area, great thermal stability, good catalytic performance, regularly arranged pore structure, tunable and accessible pores, controlled morphology, non‐toxicity, and low preparation cost …”