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Due to an increasing gap between the demand and supply, the catalytic coupling of ethanol has regained the attention of the scientific and industrial community as an "on-purpose" production route to butadiene. The most promising systems are based on bifunctional catalysts, comprising of metal sites that can dehydrogenate ethanol to acetaldehyde, and Lewis acid sites that catalyze the aldol condensation between two aldehyde molecules, as well as the Meerwein-Ponndorf-Verley (MPV) reduction of the intermediate crotonaldehyde. Here, we investigate the role of Ag in an established Ag-Zr-BEA catalyst using modulated operando DRIFTS-MS experiments. We obtain insights into the complex reaction network that involves several consecutive and parallel reactions. Based on our investigations, we formulate suggestions for catalyst optimization.

Hexagonal boron nitride (hBN) is presented as an outstanding catalyst for the selective production of C4 olefins by the oxidative dehydrogenation of n-butane and isobutane. Unlike catalysts reported previously, hBN limits the amount of undesired COx and instead forms C2 and C3 olefins as the main side products. Kinetic experiments suggest a mechanism in which the rates of n-butane and isobutane consumption are dependent on O2 adsorption. Kinetic and spectroscopic insights are used to formulate mechanistic hypotheses for the formation mechanisms of C2–C4 olefins.

Snβ zeolites are amongst the most effective heterogeneous catalysts for the Baeyer-Villiger (BV) oxidation of ketones with aqueous hydrogen peroxide (H2O2). The high selectivity is rooted in the activation of the carbonyl substrate through interaction with the isolated SnIV-sites. However, these sites are also accessible to other molecules in the reaction mixture (in particular the co-solvent and product). In this contribution, we report on the impact of competitive adsorption on the Snβ-catalyzed BV oxidation of cyclohexanone with aqueous H2O2. We furthermore prepared a series of Snβ zeolites with varying amounts of framework silanols and quantified their hydrophilicities with water adsorption and IR experiments. By correlating the results with catalytic data, we show that Snβ zeolites with an intermediate hydrophilicity achieve the highest activity. Our adaptable post-synthetic synthesis allows us to tune the material synthesis, resulting in enhanced activity compared to conventional hydrothermal Snβ.

The front cover artwork for Issue 20/2015 is provided by the Hermans research group at the University of Wisconsin-Madison (formerly located at the Swiss Federal Institute of Technology, Zurich). The image shows silica-supported Lewis acidic SnIV sites that are tuned to be catalytically active in the Meerwein–Ponndorf–Verley reduction of cyclohexanone with 2-butanol. See the Full Paper itself at http://dx.doi.org/10.1002/cctc.201500630.

Homogeneous iridium catalysts have demonstrated exceptional catalytic activity for a number of hydrogen transfer reactions. Herein, we demonstrate the synthesis of a heterogeneous iridium catalyst supported on nanoparticulate cerium oxide and investigate its application for the aerobic oxidation of benzyl alcohol and the Meerwein–Ponndorf–Verley transfer hydrogenation of cyclohexanone. Along with the optimisation of the activity of the catalyst, the kinetic parameters have been examined to unravel the elementary reaction steps mediated by this catalyst and further rationalise the observed structure–activity relationships. Both spectroscopic and catalytic investigations suggest that iridium oxide nanoparticles, most likely Ir2O3, mediate these reactions via the formation of metal hydroxide species, which are subsequently reoxidised with either a molecular oxygen or a ketone. In contrast to many other metal- or metal oxide-based catalysts, this catalyst can perform the selective oxidation of alcohols in the absence of a base, at mild temperatures and at a low metal loading.

Boron nitride was recently identified as a highly selective catalyst for the oxidative dehydrogenation of propane (ODHP). In this communication we report that other boron-containing materials such as boron carbide, titanium boride, nickel boride, cobalt boride, hafnium boride and tungsten boride, as well as elemental boron itself show the same exceptional behavior as boron nitride. X-ray photoelectron and infrared spectroscopy suggest oxyfunctionalization of the surface. This observation disproves previous mechanistic hypotheses that edge sites on the boron nitride would be the active sites and rather suggests the formation of an analogous surface-stabilized BOx active site for all tested boride catalysts.