Vita A. Kondratenko

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.

Tailored Noble Metal Nanoparticles on γ‐Al2O3 for High Temperature CH4 Conversion to Syngas

The simple deposition of tailored Rh or Pt nanoparticles (NP) on γ‐Al2O3 results in active, selective, and stable catalysts for partial oxidation of methane (POM) to syngas. The NP were prepared by the ethylene glycol method in strong alkaline solution. This approach was found to be a promising way of providing active metallic NP for catalyzing the POM reaction. NP sizes determined by small angle X‐ray scattering (SAXS) in solution and by transmission electron microscopy (TEM) on alumina were very close. This result highlights the possibility of easy pre‐characterization of NP by the former method. Supported Rh NP are intrinsically more active in the POM reaction than Pt NP and also showed a superior performance compared with a conventionally prepared Rh catalyst, even if the latter had been pre‐reduced. Mechanistic investigations in the temporal analysis of products (TAP) reactor indicate that the higher selectivity of well‐defined Rh‐NP is determined by their lower activity for consecutive CO transformations.

Methane conversion into different hydrocarbons or oxygenates: current status and future perspectives in catalyst development and reactor operation

This Perspective highlights recent developments in methane conversion into different hydrocarbons and oxygenates (methanol, its derivatives, and formaldehyde) with the purpose to address the global demand for efficient and environmentally friendly production of these bulk chemicals. Our analysis identified possible directions for further research to bring the above approaches to a commercial level. As no progress in the development of catalysts for the oxidative coupling of methane could be identified, improvements are expected through reactor operation, cost- and energy-efficient methods for product separation and for providing pure oxygen. With respect to methane oxidation to methanol, further progress can also be achieved by proper catalyst design on the basis of fundamental knowledge especially gained from homogeneous and enzymatic catalysts as well as from theoretical calculations.

Non-oxidative dehydrogenation of propane, n-butane, and isobutane over bulk ZrO2-based catalysts: effect of dopant on the active site and pathways of product formation

Non-oxidative dehydrogenation (DH) of propane, n-butane, and isobutane was investigated over bare ZrO2 and binary MZrOx (M = Li, Ca, Mg, Y, Sm or La) materials. Selected samples were characterized by XRD, Raman spectroscopy, NH3 temperature-programmed desorption, IR spectroscopy and O2 titration experiments. A correlation between the rate of olefin formation and the concentration of anion vacancies formed upon reductive catalyst treatment was established. Such defects represent the catalytically active sites, which are coordinatively unsaturated Zr4+ (Zrcus) cations. From a structural viewpoint, the active Zrcus sites should have a lower coordination number than the Zrcus sites located on the top of an ideal flat surface, thus highlighting the importance of surface defects in the target reactions. However, the intrinsic activity of such sites and/or their concentration depends on the kind of dopant for ZrO2. The dopant was also shown to inhibit side reactions especially those leading to coke due to reducing the concentration of strong acidic sites related to ZrO2. Similar to an analogue of industrial K-CrOx/Al2O3 catalyst, all binary catalysts exhibited low activity for consecutive reactions of the target olefins; the desired selectivity was higher than 85% at an alkane conversion of about 30%. With respect to the feed alkane, primary selectivity (at a zero degree of alkane conversion) to the target olefin decreases in the order: C3H8, iso-C4H10, and n-C4H10. This was explained by the higher stability of surface intermediates formed from the latter two contributing to the formation of coke and 1,3-butadiene, respectively.

Catalytic Abatement of Nitrous Oxide Coupled with Functionalization of C1–C3 Alkanes

Mechanistic aspects of selective reduction of N2O by C1–C3 alkanes resulting in N2, olefins, and hydrogen over CaO‐based catalysts were studied by combining catalytic tests at ambient pressure with transient analysis of products in high vacuum with microsecond time resolution. In the frame of this reaction, oxygen species formed from N2O participate in selective (olefin production) and nonselective (COx formation) heterogeneous interactions. The coverage by these species and the interplay of exothermic heterogeneous (N2O decomposition and oxidative alkane conversions) and endothermic homogeneous (thermal nonoxidative dehydrogenation and cracking of hydrocarbons) reaction pathways determine the overall olefin selectivity.

Unraveling the H2 Promotional Effect on Palladium-Catalyzed CO Oxidation Using a Combination of Temporally and Spatially Resolved Investigations

The promotional effect of H2 on the oxidation of CO is of topical interest, and there is debate over whether this promotion is due to either thermal or chemical effects. As yet there is no definitive consensus in the literature. Combining spatially resolved mass spectrometry and X-ray absorption spectroscopy (XAS), we observe a specific environment of the active catalyst during CO oxidation, having the same specific local coordination of the Pd in both the absence and presence of H2. In combination with Temporal Analysis of Products (TAP), performed under isothermal conditions, a mechanistic insight into the promotional effect of H2 was found, providing clear evidence of nonthermal effects in the hydrogen-promoted oxidation of carbon monoxide. We have identified that H2 promotes the Langmuir–Hinshelwood mechanism, and we propose this is linked to the increased interaction of O with the Pd surface in the presence of H2. This combination of spatially resolved MS and XAS and TAP studies has provided previously unobserved insights into the nature of this promotional effect.