Heterogeneous Hydrogenation Catalysts Based on Quartz

Comparative Density Functional Theory Study of Cinchonidine and Hydrogen Coadsorption on Platinum Group Metals (Rh, Ir, Pd, and Pt) and Its Implications on Surface Chiral Site Formation

“…Therefore, various strategies have been developed to impart chirality to catalytically active materials. − A practicable and simple method is the adsorptive anchoring of suitable organic chiral auxiliaries on the catalyst surface. Prominent examples are cinchona-modified platinum for the asymmetric hydrogenation of activated ketones, − and palladium − ,,,− for the asymmetric hydrogenation of prochiral olefins. In the past decades considerable effort has been made to expand this concept to other platinum group (PG) metals, employing various chiral organic modifiers. ,,, Overall these research efforts on practical catalysts have led to a significant extension of the scope of substrates and a better understanding of the reaction mechanisms.…”

“…Typical for catalysts based on this concept is their high specificity. Subtle changes in the catalyst properties, the structure of substrate and modifier and their adsorption modes, as well as reaction conditions (solvent, hydrogen pressure, modifier concentration, and temperature) generally result in changes of enantioselectivity and activity. − ,− Recently, a striking influence of the orientation of the chiral modifier on its enantio-differentiating power has been demonstrated by means of attenuated total reflection-infrared (ATR-IR) and UV–vis operando spectroscopic studies using the asymmetric hydrogenation of 4-methoxy-6-methyl-2-pyrone over cinchonine-modified Pd/TiO 2 as a model reaction . While the adsorption of cinchona alkaloids on Pt − and Pd , has been in the focus of several studies, similar studies on other PG metals are scarce. , In particular, there is a lack of knowledge about the effect of hydrogen coadsorption on the adsorption geometry of cinchona alkaloids.…”

Direct Synthesis of in-Situ Chirally Modified Palladium Nanocrystals without Capping Agents and Their Application in Heterogeneous Enantioselective Hydrogenations

“…The increasing demand of optically pure compounds in pharmaceutical, agrochemical, and perfume industries has provided tremendous impetus for developing efficacious synthetic methods for the preparation of single-enantiomer chiral products . Heterogeneous asymmetric hydrogenation of prochiral chemicals with CC or CO bonds is an ideal way to synthesize important chiral products due to its significant economic and ecological advantages. − To date, chirally modified supported metal catalysts are most extensively studied for heterogeneous enantioselective hydrogenations. − However, the difference between the energy of S and R transition states in heterogeneous asymmetric catalysis is the same as the range of various weak interactions existing on the surface of the support (e.g., hydrogen bond, physical adsorption, and van der Waals force) . Baiker and co-workers found that the chemoselectivity and the enantioselectivity are both greatly affected by adjusting the basicity and acidity of the support .…”

“…Chiral modifiers, such as cinchona alkaloids and chiral amino acids, also contain specific functional groups (e.g., amino or carboxyl groups), which could bind on the metal surface like conventional capping agents. − ,, Bönnemann and Braun applied dihydrocinchonidine to stabilize colloidal Pt nanoparticles, and the nanoparticle size of Pt can be varied from 1.5 to 4 nm by changing the ratio between platinum and dihydrocinchonidine during the synthesis . This system showed remarkable enantioselectivity in CO bond hydrogenation of ethyl pyruvate. , Therefore, the chiral modifiers are possible to be used as a new category of shape-control agents in the preparation of metal nanocrystals, which can not only stabilize the metal particles but also control the morphology and exposed facets of metal nanocrystals.…”

Preparation of Pd-Loaded Hierarchical FAU Membranes and Testing in Acetophenone Hydrogenation

“…Reduction processes are among the prevalent transformations in organic chemistry and are widely applied in industrially relevant practices [1]. In the pharmaceutical and biotechnological industries, the synthesis processes for the preparation of a wide range of compounds often imply the conversion of functional groups, the reduction of a carbonyl moiety to the corresponding alcohol being one of the most commonly required intermediary transformations [2,3]. On the industrial scale, however, many well-established and routinely applied technologies for carbonyl reduction need to be revised to meet the more stringent standards of safety and efficiency currently imposed by regulatory agencies in many countries worldwide.…”