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In the last few years, researchers have focused their attention on the synthesis of new catalyst structures based on or inspired by nature. Biotemplating involves the transfer of biological structures to inorganic materials through artificial mineralization processes. This approach offers the main advantage of allowing morphological control of the product, as a template with the desired morphology can be pre-determined, as long as it is found in nature. This way, natural evolution through millions of years can provide us with new synthetic pathways to develop some novel functional materials with advantageous properties, such as sophistication, miniaturization, hybridization, hierarchical organization, resistance, and adaptability to the required need. The field of application of these materials is very wide, covering nanomedicine, energy capture and storage, sensors, biocompatible materials, adsorbents, and catalysis. In the latter case, bio-inspired materials can be applied as catalysts requiring different types of active sites (i.e., redox, acidic, basic sites, or a combination of them) to a wide range of processes, including conventional thermal catalysis, photocatalysis, or electrocatalysis, among others. This review aims to cover current experimental studies in the field of biotemplating materials synthesis and their characterization, focusing on their application in heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

This article explores the effect of the synthetic method of titanium dioxide (TiO2)/C composites (physical mixture and the water-assisted/unassisted sol-gel method) on their photocatalytic activity for hydrogen production through glycerol photoreforming. The article demonstrates that, apart from a high surface area of carbon and the previous activation of its surface to favor titania incorporation, the appropriate control of titania formation is crucial. In this sense, even though the amount of incorporated titania was limited by the saturation of carbon surface groups (in our case, ca. 10 wt.% TiO2), the sol-gel process without water addition seemed to be the best method, ensuring the formation of small homogeneously-distributed anatase crystals on mesoporous carbon. In this way, a ca. 110-fold increase in catalyst activity compared to Evonik P25 (expressed as hydrogen micromole per grams of titania) was achieved. [ABSTRACT FROM AUTHOR]

In the present piece of research, hydrogen production via the photo-reforming of glycerol (a byproduct from biodiesel generation) is studied. Catalysts consisted of titania modified by Ni (0.5% by weight) obtained through deposition–precipitation or impregnation synthetic methods (labelled as Ni-0.5-DP and Ni-0.5-IMP, respectively). Reactions were performed both under UV and solar irradiation. Activity significantly improved in the presence of Ni, especially under solar irradiation. Moreover, pre-reduced solids exhibited higher catalytic activities than untreated solids, despite the "in-situ" reduction of nickel species and the elimination of surface chlorides under reaction conditions (as evidenced by XPS). It is possible that the catalyst pretreatment at 400 °C under hydrogen resulted in some strong metal–support interactions. In summary, the highest hydrogen production value (ca. 2600 micromole H2·g−1) was achieved with pre-reduced Ni-0.5-DP solid using UV light for an irradiation time of 6 h. This value represents a 15.7-fold increase as compared to Evonik P25. [ABSTRACT FROM AUTHOR]

Abstract: The liquid-phase hydrodechlorination of 3-chloropyridine and chlorobenzene has been studied over alkali-modified zirconia-supported palladium catalysts. The modification of the ZrO2 with alkali metal carbonates improves the catalytic activity of the final palladium catalyst. Therefore, the larger the ionic radii (Li+ <Na+ <K+), the greater the catalytic activity (TOF) of the palladium catalyst. For 3-chloropyridine, hydrodechlorination proceeds without catalyst deactivation. This is explained as the result of the interaction of reaction products (pyridine and HCl) forming pyridinium chloride, thus avoiding the detrimental effect of HCl on the palladium particles. Catalytic hydrodechlorination of chlorobenzene over Pd catalysts exhibits an initial catalytic activity (TOF) much lower than that of 3-chloropyridine and the Pd catalysts deactivate as the reaction proceeds. Finally, chlorobenzene hydrodehalogenation has also been carried out in the presence of an equimolecular amount of pyridine resulting in a decrease in the initial reaction rate on the one hand, but also in an increase in final conversion on the other. [Copyright &y& Elsevier]

In this work, photocatalysts consisting of TiO 2 supported on zeolite (USY62) were synthesized by sol-gel method and, subsequently, a noble metal (Pt, Au, or Ag) was incorporated by impregnation or photodeposition. Zeolite-TiO 2 composites were characterized by SEM, TEM, XRD, N 2 adsorption-desorption, Raman and UV–vis spectroscopy, and well-dispersed anatase TiO 2 particles (ca. 10 nm) that exhibited a blue-shift in the UV–vis absorption due to the size quantization effect were produced. The photocatalytic activity of all zeolite-TiO 2 composites was examined by the photoreforming of aqueous glycerol solution (10% w/w) under UV and solar-simulated radiation. The activity of the zeolitic photocatalysts decreased in the order Pt > Au > Ag, being catalysts prepared by photodeposition more active than those prepared by impregnation. Moreover, Zeolite-supported TiO 2 , led to a TiO 2 with smaller deactivation in H 2 production than unsupported TiO 2 , which can be ascribed to the small TiO 2 particle size or an interaction zeolite-TiO 2. All in all, a photocatalyst (USY-Ti-PPt) with TiO 2 up to four times more active than unsupported TiO 2 under UV radiation was prepared. [Display omitted] • Zeolite-supported TiO 2 of ca. 10 nm was prepared by sol-gel method • Zeolite structure was maintained after the incorporation of TiO 2 and noble metal • H 2 production via glycerol photoreforming was studied on zeolite-TiO 2 composites • Supported TiO 2 was up to 4-times more active than unsupported TiO 2 in H 2 production • Zeolite-supported TiO 2 had a smaller deactivation than TiO 2 in H 2 production [ABSTRACT FROM AUTHOR]

Several pure magnesium oxides together with some mixed systems (magnesia–titania and magnesia–zirconia) were synthesised, using the sol–gel technique. Chemical, textural and structural characterisation of the solids was carried out through a wide range of physical techniques. In all the cases, the presence of titanium or zirconium led to an increase in surface area as compared to pure magnesia. X-ray diffraction (XRD) revealed that no mixed phases were observed, but MgO (periclase), TiO2 (anatase) and ZrO2 (tetragonal) phases. As for mixed oxides, surface and bulk composition is quite similar in Mg–Zr system, whereas titanium tends to accumulate in the surface of Mg–Ti solids. The surface of the catalysts appears clearly carbonated as revealed by the XPS and diffuse reflectance infrared (DRIFT) spectra, revealing the basic character of the catalysts prepared. [Copyright &y& Elsevier]

Several magnesium containing catalysts were tested for the 2-methyl-3-butyn-2-ol (MBOH) test reaction in a microcatalytic pulse reactor. All solids showed a selectivity close to 100% toward products formed on basic sites (mainly acetone and acetylene) in the 433–623 K range. However, no correlation was found between molar conversion per gram of catalyst and basic site density, determined by temperature-programmed desorption–mass spectrometry of CO2 as the probe molecule. In the search for a process that fulfilled such a correlation, a new model reaction for base catalysts was found: isomerization of 3-phenyl-1-propene (allylbenzene) to 1-phenyl-1-propene (cis+trans). Therefore, a good correlation (r=0.986) between molar conversion (per gram of catalyst) and basic site density was obtained at 523 K for all catalysts tested. [Copyright &y& Elsevier]