In situ formation of ZnOx species for efficient propane dehydrogenation.

Propane dehydrogenation (PDH) to propene is an important alternative to oil-based cracking processes, to produce this industrially important platform chemical1,2. The commercial PDH technologies utilizing Cr-containing (refs. 3,4) or Pt-containing (refs. 5-8) catalysts suffer from the toxicity of Cr(VI) compounds or the need to use ecologically harmful chlorine for catalyst regeneration9. Here, we introduce a method for preparation of environmentally compatible supported catalysts based on commercial ZnO. This metal oxide and a support (zeolite or common metal oxide) are used as a physical mixture or in the form of two layers with ZnO as the upstream layer. Supported ZnOx species are in situ formed through a reaction of support OH groups with Zn atoms generated from ZnO upon reductive treatment above 550 °C. Using different complementary characterization methods, we identify the decisive role of defective OH groups for the formation of active ZnOx species. For benchmarking purposes, the developed ZnO-silicalite-1 and an analogue of commercial K-CrOx/Al2O3 were tested in the same setup under industrially relevant conditions at close propane conversion over about 400 h on propane stream. The developed catalyst reveals about three times higher propene productivity at similar propene selectivity.

1,3-Thia-zole-4-carbo-nitrile.

The title compound, C4H2N2S, is a 1,3-thia-zole substituted in the 4-position by a nitrile group. In the crystal, C-H⋯N hydrogen bonds and aromatic π-π stacking inter-actions are observed.

Control of coordinatively unsaturated Zr sites in ZrO2 for efficient C-H bond activation.

Due to the complexity of heterogeneous catalysts, identification of active sites and the ways for their experimental design are not inherently straightforward but important for tailored catalyst preparation. The present study reveals the active sites for efficient C-H bond activation in C1-C4 alkanes over ZrO2 free of any metals or metal oxides usually catalysing this reaction. Quantum chemical calculations suggest that two Zr cations located at an oxygen vacancy are responsible for the homolytic C-H bond dissociation. This pathway differs from that reported for other metal oxides used for alkane activation, where metal cation and neighbouring lattice oxygen form the active site. The concentration of anion vacancies in ZrO2 can be controlled through adjusting the crystallite size. Accordingly designed ZrO2 shows industrially relevant activity and durability in non-oxidative propane dehydrogenation and performs superior to state-of-the-art catalysts possessing Pt, CrOx, GaOx or VOx species.

Unexpectedly high activity of bare alumina for non-oxidative isobutane dehydrogenation.

Bare alumina shows surprisingly high activity in non-oxidative dehydrogenation of isobutane to isobutylene. The activity is related to surface coordinatively unsaturated Al sites (Alcus), which are created upon removal of OH groups during alumina treatment at high temperatures. Alcus and neighbouring lattice oxygen represent the active site for isobutane dehydrogenation.

Bulk binary ZrO2-based oxides as highly active alternative-type catalysts for non-oxidative isobutane dehydrogenation.

Bulk binary ZrO2-based oxides efficiently catalyse non-oxidative dehydrogenation of isobutane to isobutylene. Their activity strongly depends on the kind of second metal oxide. So designed CrZrOx showed superior activity to industrially relevant catalysts with supported Pt or CrOx species. It was also stable under alternating dehydrogenation and oxidative regeneration cycles over ca. 110 h under different reaction conditions between 550 and 600 °C.

ZrO2 -Based Alternatives to Conventional Propane Dehydrogenation Catalysts: Active Sites, Design, and Performance.

Non-oxidative dehydrogenation of propane to propene is an established large-scale process that, however, faces challenges, particularly in catalyst development; these are the toxicity of chromium compounds, high cost of platinum, and catalyst durability. Herein, we describe the design of unconventional catalysts based on bulk materials with a certain defect structure, for example, ZrO2 promoted with other metal oxides. Comprehensive characterization supports the hypothesis that coordinatively unsaturated Zr cations are the active sites for propane dehydrogenation. Their concentration can be adjusted by varying the kind of ZrO2 promoter and/or supporting tiny amounts of hydrogenation-active metal. Accordingly designed Cu(0.05 wt %)/ZrO2 -La2 O3 showed industrially relevant activity and durability over ca. 240 h on stream in a series of 60 dehydrogenation and oxidative regeneration cycles between 550 and 625 °C.

An innovative approach for highly selective direct conversion of CO2 into propanol using C2H4 and H2.

Multifunctional catalysts are developed for converting CO2 with C2H4 and H2 into propanol. Au nanoparticles (NP) supported on TiO2 are found to facilitate this reaction. The activity and selectivity strongly depend on NP size, which can be tuned by the method of Au deposition and by promoting with K. The promoter improves the selectivity to propanol. Under optimized reaction conditions (2 MPa, 473 K, and CO2/H2/C2H4=1:1:1), CO2 is continuously converted into propanol with a near-to-100% selectivity. Catalytic tests as well as mechanistic studies by in situ FTIR and temporal analysis of products with isotopic tracers allow the overall reaction scheme to be determined. Propanol is formed through a sequence of reactions starting with reverse water-gas shift to reduce CO2 to CO, which is further consumed in the hydroformylation of ethylene to propanal. The latter is finally hydrogenated to propanol, while propanol hydrogenation to propane is suppressed.

Optimization of catalysts using specific, description-based genetic algorithms.

This paper deals with the key optimization task that has to be solved when improving the performance of many chemical processes--optimization of the catalysts used in the reaction via the optimization of its composition and preparation. A novel approach is presented that allows for the preservation of the advantages of genetic algorithms developed specifically for the optimization of catalytic materials but avoids the disadvantageous necessity to reimplement the algorithm when the scope of the optimized materials changes. Its main idea is to automatically generate problem-tailored implementations from requirements concerning the materials with a program generator. For the specification of such requirements, a formal description language, called catalyst description language, has been developed.