The Effect of Outer‐Sphere Acidity on Chemical Reactivity in a Synthetic Heterogeneous Base Catalyst

Abstract

Rationales Design der äußeren Oberfläche kann zur Optimierung von heterogenen Katalysatoren genutzt werden. Durch molekulares Prägen von Siliciumdioxid wurden so aktive Stellen mit hydrophilen (1) und hydrophoben Umgebungen (2) erzeugt. Die Knoevenagel‐Kondensation von Isophthalaldehyd mit Malonitril verlief mit 1 etwa 50‐ oder 30‐mal schneller als mit 2 bzw. einem kommerziellen Katalysator aus einer Monoschicht von 3‐Aminopropylgruppen auf Silliciumdioxid.

Catalytic consequences of open and closed grafted Al(III)-calix[4]arene complexes for hydride and oxo transfer reactions

“…Previous comparisons of trimethylsilyl (TMS)-capped and native silanolcontaining Ti-on-silica olefin epoxidation catalysts show a lack of appreciable activity or selectivity difference under dry conditions, when using organic hydroperoxide as oxidant (45). Because such TMS capping is known to block virtually all accessibility of silanols to serve as hydrogen bond donors (46), this result suggests that either organic hydroperoxide or alcohol byproduct can serve at least as an effective hydrogen bond donor as a surface silanol for decreasing the barrier for oxygen transfer. [4]arene bond breaking at the transition state for the closed active site 12.…”

Catalytic Partial Oxidation of Methanol and Ethanol for Hydrogen Generation

“…Their lithographic techniques [213][214][215] in nanoparticle array synthesis and seedless polyol methods [216] for nanotube preparation showed efficient ways to control the size and shape of active sites. Other approaches such as outer-sphere control [217,218] and strong electrostatic adsorption [219,220] developed by other groups also shed light on architectures of heterogeneous catalysts. A Review detailing the state-of-the-art approaches in synthesizing nanoparticles and heterogeneous catalysts was just published.…”

Tuning acid–base cooperativity to create next generation silica-supported organocatalysts

“…Other weak acids have been shown to accelerate the aldol and related reactions, including the surface silanols of inorganic silica [20,25,26,67]. These weakly acidic surface silanols interact only weakly with the base, and therefore, do not inhibit the base from catalyzing the reaction, but rather increase the conversion compared to reactions with base alone.…”