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Abstract. Palladium nano particles in tetrahedral (Td), octahedral (Oh) and spherical (Sp) shapes, supported on hydrotalcite, were synthesized and characterized by XRD and TEM. Td shaped Pd nano particles, with maximum number of exposed (111) planes of Pd, display maximum turn over frequency (TOF) / intrinsic activity for hydrogenation of cinnamaldehyde, indicating the importance of active site geometry. Oh & Sp shaped Pd nano particles that expose both (111) and (100) planes have relatively lower intrinsic activity. For a given reaction, it is essential that appropriate active site geometry, as dictated by the shape/morphology of nano particles be made available. Synthesis and stabilization of such shape controlled nano particles is of prime importance in developing catalysts with higher activity.Keywords: Pd nano particles, shape control, active site geometry, cinnamaldehyde, hydrogenation, TOF. IntroductionSupported metal catalysts have been extensively studied, as they display high activity, selectivity, stability under mild reaction conditions as required in many catalytic reactions [1]. A number of factors are known to influence the performance of supported metal catalysts [2], namely, the metal loading, nature of metals, crystallite size, metal surface morphology, nature of the support, addition of second/promoter elements [3], the metal-support interactions and method of preparation [4]. Of these, the crystallite size and morphology of the metal particles are the two important factors affecting the number and nature/geometry of the active sites, which in turn influence activity and selectivity respectively. Nano size metal particles with different sizes and shapes have different degrees of dispersion, exposed facets and fractions of atoms located at different corners, edges, and defects, each having specific activity/selectivity. Thus, for a given reaction, the catalytic activity of particles with different morphology can vary significantly. Semagina and Kiwi-Minsker [5] compared the activity of nano size Pd hexagons and spheres for hydrogenation of 2-methyl-3-butyn-2-ol and observed that nano spheres with maximum amount of exposed (111) planes displayed highest TOF. Role of shaped Pd nano crystals in controlling activity & selectivity for various reactions by influencing the facets, and relative populations of atoms in edges, corners and planes has been reviewed in detail by Zhang et al [6]. Wang et al. [7] reported that silica supported Pd nano particles in octahedral shape (with predominantly (111) planes) was more active for CO oxidation compared to cubic Pd (with (100) facet) while the facet activity pattern was exactly reverse in the case of silica supported Pt. Hence, studies on the preparation, characterization and performance evaluation of shape controlled supported metal catalysts has been area of tremendous importance both from basic as well as applied aspects of catalysis. In the present work, we have explored the effect of Pd nano particles in tetrahedral (Td), octahedral (Oh) and spherical ...

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The catalytic activity of nickel nanoparticles (5% Ni w/w loading) dispersed on different metal oxide supports has been explored for the hydrogenation of furfural. Nickel, supported on reducible oxides (CeO2 and TiO2), displays higher (almost 100%) conversion compared to that on non‐reducible oxide supports (SiO2, Al2O3, Mg3AlOx). H2‐TPR and XPS analyses bring out the influence of metal‐support interaction during the reduction of nickel precursor and their electronic properties. The adsorption and activation of furfural on the catalyst has been studied using infrared spectra and DFT calculations. The reaction proceeds via both ring‐rearrangement and ring hydrogenation pathways, with furfuryl alcohol as the primary intermediate. At higher reaction temperature, reducible oxide supported catalysts, particularly titania, favours deep‐hydrogenated products and higher conversion than non‐reducible oxide supported catalysts. Among all the catalysts, nickel on titania displayed maximum conversion of furfural. TiO2 possessing higher acidity than ceria, favoured ring‐rearrangement of furfuryl alcohol to cyclopentanone at high temperatures, while the latter retarded reduction of cyclopentanone due to blockage of active‐sites by unreacted furfural and strongly adsorbing intermediates. The combined effects of the electronic‐state of supported metal and surface acidity of catalyst provide a new strategy to tune catalytic properties for selective transformation during hydrogenation of furfural.