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• Pt/TiO 2 catalysts with different Pt aggregation sizes were prepared. • Hydrogenation activity of Pt/TiO 2 showed a volcano-shaped trend with Pt sizes. • Pt activity ranks in the order of nanometer cluster > nanoparticle > single atom. • Relationships between Pt activity and structural/electronic property were discussed. Supported metal catalysts often consist of metal sites ranging from nanoparticles to subnanometer clusters and single atoms. It remains a necessity to differentiate these sites to guide design of optimal catalysts. Here we report a simple method to assess the distribution of metal active sites in catalyst samples. The method takes the advantage of the structure sensitivity of styrene hydrogenation over titania supported platinum (Pt) catalysts with Pt aggregates varied from single atom to ∼1.40 nm nanoparticles. The physicochemical properties were characterized by STEM, XPS, XANES, H 2 -TPR and CO-chemisorption measurements. The reactivity of Pt sites was quantified by styrene hydrogenation at ambient conditions. The nanometer-sized Pt clusters have significantly higher activity than Pt nanoparticles, sub-nanometer clusters or isolated single atoms. The relationship between activity and structural/electronic properties of Pt sites influenced by particle sizes was discussed. Similar relationship was found in the carbon supported Pt catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

Lead substituted hydroxyapatite (Pb-HAP) has been an active catalyst for oxidative coupling of methane (OCM) reactions. CO 3 2 − substituted HAP (HAP-CO 3 ) has showed enhanced oxide ion conductivity than bare HAP in high temperature solid oxide fuel cells. Substitutions for both cations and anions in HAP structure (Pb-HAP-CO 3 ) are promising to integrate the catalytic property of Pb-HAP and oxide ion conductive property of HAP-CO 3 into one apatite-based ceramic material that can be manufactured into membrane reactors for possessing CH 4 activation and O 2 permeation capabilities for efficient OCM reactions. In this work, the effects of substitutions for both cation (Pb 2+ ) and anion (CO 3 2 − ) in HAP structure on OCM reactions were studied. The composition and physicochemical properties of HAP catalysts were changed by the cation and anion substitutions, respectively, and as consequences, they influenced the catalytic performances of HAP structure in OCM reactions. The selectivity to C 2 (ethylene and ethane) products increased in the order of HAP-CO 3 < HAP < Pb-HAP-CO 3 < Pb-HAP, while Pb-HAP-CO 3 showed the best stability and comparable C 2 yield (under optimized reaction conditions) to Pb-HAP catalyst. Under different reaction temperature and/or CH 4 /O 2 ratio in the OCM reactions, the CH 4 conversion and C 2 or CO x (CO and CO 2 ) selectivity showed a strong dependence on the composition of HAP-based catalysts. The present study forms a basis for understanding of the correlations between the composition, structure, and catalytic performance of HAP and other apatite structured catalysts, which are potential membrane materials for OCM reactions in membrane reactors. [ABSTRACT FROM AUTHOR]

• Catalytic performance of metal (Ga or Zn)-loaded mesoporous lamellar zeolites was evaluated. • Mesoporous lamellar structure is pivotal in determining metal dispersion in zeolite catalyst. • Metal loading changes the acidity of the zeolite catalyst and effect of Zn is more pronounced compared to Ga. • Higher liquid aromatics yield and selectivity for mono-benzene alkylated aromatics was observed while less coke was formed. • Both zeolite structure (mesoporosity) and type of metal dopant affect the catalytic performance of catalyst. The effects of meso-/microporous structure and metal-modification with gallium or zinc on catalytic performances of lamellar MFI zeolites in ethylene conversion reaction to liquid aromatics were investigated. TEM, XRD, Ar adsorption-desorption, UV-Visible spectroscopy, and H 2 -TPR measurements showed that the zeolite structure is a pivotal factor for controlling the type of metal dopant species forming on zeolite, their size, and their distribution. Adding metal dopants to zeolite structure decreased the Brønsted to Lewis (B/L) acid site ratio in the zeolites and improved their catalytic performance. As a result, metal-modified lamellar MFI zeolites showed higher liquid aromatics yield and selectivity for mono-benzene alkylated aromatics and lower coke formation rate compared to their microporous commercial MFI analogies. Zinc-loaded lamellar MFI had the most efficient catalytic performance among all studied catalysts. This phenomenon can be explained by higher accessibility of reactants to active sites and facilitated transport of products from lamellar structure of this zeolite and the low B/L acid site ratio of this catalyst provided by metal-modification, which is more suitable for ethylene aromatization. A bifunctional reaction mechanism has been proposed based on the analysis results of reaction product distributions that demonstrates the effect of both zeolite acid sites and metal sites in conversion of ethylene to liquid aromatics over MFI zeolite catalysts. [ABSTRACT FROM AUTHOR]