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A novel process for the direct ammoxidation of propane over steam-activated Fe-silicalite at 723–823 K is reported. Yields of acrylonitrile (ACN) and acetonitrile (AcCN) below 5% were obtained using N2O or O2 as the oxidant. Co-feeding N2O and O2 boosts the performance of Fe-silicalite compared to the individual oxidants, leading to AcCN yields of 14% and ACN yields of 11% (propane conversions of 40% and products selectivity of 25–30%). The beneficial effect of O2 on the propane ammoxidation with N2O contrasts with other N2O-mediated selective oxidations over iron-containing zeolites (e.g. hydroxylation of benzene and oxidative dehydrogenation of propane), where a small amount of O2 in the feed dramatically reduces the selectivity to the desired product. It is shown that the productivity of ACN and especially AcCN, expressed as mol product h−1 kg, is significantly higher over Fe-silicalite than over active propane ammoxidation catalysts reported in the literature. Our results open new perspectives to improve the performance of alkane ammoxidation catalysts. [ABSTRACT FROM AUTHOR]

For elucidating the mechanistic aspects of oxygen formation during N2O decomposition over commercial woven Pt–Rh gauze, transient experiments were carried out in the temporal analysis of products (TAP) reactor by pulsing N216O over 18O-pretreated gauze catalyst at temperatures typical of industrial ammonia burners (1073–1273 K). The transient responses of N2O and the products of its decomposition (O2 and N2) were fitted to two different mechanistic models. From the isotopic studies and the fitting of transient experiments, two separate routes of oxygen formation during catalytic N2O decomposition have been identified. Oxygen is produced via both (i) interaction of N2O with adsorbed oxygen species formed from N2O and (ii) recombination of adsorbed oxygen species on the catalyst surface. The relative contribution of these reaction pathways depends on the reaction temperature. [ABSTRACT FROM AUTHOR]

The article offers the author's insights on several research studies on the technological significance of zeolite. The author cites the study conducted by S. Mintova and colleagues which have found that the control of crystallization over its early stages is essential to classify important nanosized metastable phases. He mentions the study lead by W. Schwieger, who takes different approach to determine the industrial applications of zeolites, in which it proved that the introduction of 3-(trimethoxysilyl) propyl hexadecyl dimethyl ammonium chloride (TPHAC) and amphiphilic organosilane surfactant in the synthesis gel results to a house-of-cards-like arrangement of zeolite X nanosheet.

Recently discovered phosphate-derived Ni catalysts have opened a new pathway towards multicarbon products via CO2 electroreduction. However, understanding the influence of basic parameters such as electrode potential, pH, and buffer capacity is needed for optimized C3+ product formation. To this end, rigorous catalyst evaluation and sensitive analytical tools are required to identify potential new products and minimize increasing quantification errors linked to long-chain carbon compounds. Herein, we contribute to enhance testing accuracy by presenting sensitive 1H NMR spectroscopy protocols for liquid product assessment featuring optimized water suppression and reduced experiment time. When combined with an automated NMR data processing routine, samples containing up to 12 products can be quantified within 15 min with low quantification limits equivalent to Faradaic efficiencies of 0.1%. These developments disclosed performance trends in carbon product formation and the detection of four hitherto unreported compounds: acetate, ethylene glycol, hydroxyacetone, and i-propanol. Phosphate-derived nickel catalysts enable access to multicarbon products via CO2 electroreduction, but it remains unclear how operating conditions influence product formation. Here, refined 1H NMR spectroscopy protocols are introduced and combined with an automated NMR data processing routine, enabling quantification of carbon product formation as a function of various parameters. [ABSTRACT FROM AUTHOR]

The gas-phase aldol condensation of propanal, taken as model for the aldehyde components in bio-oils, has been studied with a combined operando set-up allowing to perform FT-IR & UV-Vis diffuse reflectance spectroscopy (DRS) with on-line mass spectrometry (MS). The selected solid base catalysts, a cesium-exchanged X zeolite (Cs-X), a calcium hydroxyapatite (Ca-HA) and two alkaline metal-grafted ultrastable Y (Na- and Rb-USY) zeolites, were characterized ex-situ by FT-IR after CO (CO-IR) and pyridine (Py-IR) adsorption and subsequent desorption. The combined operando spectroscopy study shows that alkaline metal-grafted USY zeolites are the most selective catalysts towards aldol dimer product formation, while the hydroxyapatite was more selective for successive aldol condensation reactions. For Na-USY and Rb-USY, the C-C coupling seems to be the rate-determining step during the surface reaction, which is the limiting stage of the overall catalytic process. In contrast, for the two more basic catalysts, i.e., Cs-X and Ca-HA desorption is limiting the overall catalytic process. Furthermore, the combined operando FT-IR & UV-Vis DRS methodology allowed monitoring the formation of carbonaceous deposits as a function of reaction time. In particular, for Cs-X and Ca-HA the rapid formation of carbonaceous deposits was observed consisting of (poly-)aromatics and highly conjugated structures, respectively. The physicochemical properties of Ca-HA with strong basic sites and moderate acidity limit its deactivation despite the observed coke formation. On the other hand, both USY catalysts were more efficient in suppressing coke formation likely due to the moderate strength of their active sites. [ABSTRACT FROM AUTHOR]

A major challenge in the implementation of laboratory-designed catalysts is the scale-up into technically relevant forms. Advanced characterization is essential to understand and optimize catalyst assembly and function in industrial reactors. This Article presents an integrated approach to visualizing millimetre-sized extrudates and granules of a hierarchical MFI-type zeolite, displaying trimodal networks of micropores (0.56 nm), intracrystalline mesopores (?10 nm) and macropores (?200-300 nm). As exemplified for the conversion of methanol to olefins, the hierarchical zeolite yields a superior performance compared to its conventional analogue. The combination of dedicated specimen preparation with state-of-the-art optical, X-ray and electron-based microscopic and tomographic techniques proves a powerful methodology to reveal otherwise inaccessible information regarding structural organization over the whole range of length scales. It is expected that these tools will play a crucial role in the rationalization of scale-up principles in catalyst development. [ABSTRACT FROM AUTHOR]

In heterogeneous catalysis, rates with Arrhenius-like temperature dependence are ubiquitous. Compensation phenomena, which arise from the linear correlation between the apparent activation energy and the logarithm of the apparent pre-exponential factor, are also common. Here, we study the origin of compensation and find a similar dependence on the rate-limiting surface coverage term for each Arrhenius parameter. This result is derived from an experimental determination of the surface coverage of oxygen and chlorine species using temporal analysis of products and prompt gamma activation analysis during HCl oxidation to Cl2 on a RuO2 catalyst. It is also substantiated by theory. We find that compensation phenomena appear when the effect on the apparent activation energy caused by changes in surface coverage is balanced out by the entropic configuration contributions of the surface. This result sets a new paradigm in understanding the interplay of compensation effects with the kinetics of heterogeneously catalysed processes. [ABSTRACT FROM AUTHOR]

Advances in materials synthesis bring about many opportunities for technological applications, but are often accompanied by unprecedented complexity. This is clearly illustrated by the case of hierarchically organized zeolite catalysts, a class of crystalline microporous solids that has been revolutionized by the engineering of multilevel pore architectures, which combine unique chemical functionality with efficient molecular transport. Three key attributes, the crystal, the pore and the active site structure, can be expected to dominate the design process. This review examines the adequacy of the palette of techniques applied to characterize these distinguishing features and their catalytic impact. [ABSTRACT FROM AUTHOR]