No abstract

The selective hydrogenation of α,β‐unsaturated aldehydes is an ideal case for studying the structure‐activity relationships in heterogeneous catalysis. In particular, cinnamaldehyde can be used as probe molecule for revealing the competition between hydrogenation of C=C and C=O bond. Here, we investigated the effect of the modification of some Pt supported on carbon catalysts by WOx species in cinnamaldehyde hydrogenation, as WOx species are reported to increase the adsorption and activation of the C=O group of α, β‐unsaturated aldehydes. Classical techniques used for correlating the catalyst activity and the selectivity to the characteristic of the materials (XRD, HAADF‐STEM, XEDS mapping and XPS) have been coupled with NMR relaxometry, as innovative application, to disclose how the molecule approaches the catalyst surface. This indeed constitutes a crucial aspect that rule the catalytic activity. Therefore, an innovative, holistic approach has been used to consider the whole catalytic system.

The hydrogenation of muconic acid (MA) to bio-adipic acid (AdA) is one of the green chemical processes that has attracted the most interest in recent years. Indeed, MA can be readily obtained from biomass through fermentative processes. Here, we aimed to investigate the synergic effect of electronic promotion that the addition of a second metal, even in small quantities, can have on Pd-based catalyst, known for its low stability. Ni and Zn were taken into consideration and two different catalysts (1%Pd8Ni2/HHT and 1%Pd8Zn2/HHT) were synthetized by sol immobilization method and supported on high-temperature, heat-treated carbon nanofibers (HHT-CNFs) that are known to enhance the stability of palladium. The catalysts were tested in MA hydrogenation and thoroughly characterized by TEM, ICP, and XPS analysis to unveil the effect of the second metal. To solve the solubility issue and have a starting material as similar as feasible to the post-fermentation conditions of the biomass, sodium muconate salt was chosen as a substrate for the reaction. All of the synthetized bimetallic catalysts showed a higher activity than monometallic Pd and better stability during the recycling tests, pointing out that even a small amount of these two metals can increase the catalytic properties of monometallic Pd.

Acetone-stabilized Au- and Sn-solvated metal atoms (SMAs) were used as to obtain Au- and AuSn-supported catalysts by simple impregnation on a reducible (TiO2) and a non-reducible (Al2O3) metal-oxide. Their catalytic behaviour was investigated for cyclohexane oxidation to cyclohexanol and cyclohexanone (KA oil), and their morphological and physical properties were studied by TEM, STEM-EDS and 119Sn-Mössbauer spectroscopy. The catalytic results firstly demonstrated that the bare supports played a role on the reaction mechanism, slowing down the formation of the oxidation products and directing the radical formation. Hereinafter, the comparison between the monometallic Au-supported catalysts and the corresponding bimetallic Au-Sn catalysts allowed for the understanding of the potential role of Sn. 119Sn-Mössbauer characterization analyses showed the presence of SnO2, which was recognized to favour the electrons’ exchange to form radicals, interacting with oxygen. Such interaction, in particular, could be favoured by the co-presence of Au. Moreover, the same metal composition on the catalyst surface resulted in a different catalytic behaviour depending on the support.