Deactivation studies of bimetallic AuPd nanoparticles supported on MgO during selective aerobic oxidation of alcohols

Abstract

Here we report the synthesis and characterisation of high surface area MgO prepared via the thermal decomposition of various magnesium precursors (MgCO3, Mg(OH)2 and MgC2O4). Bimetallic gold-palladium nanoalloy particles were supported on these MgO materials and were tested as catalysts for the solvent-free selective aerobic oxidation of benzyl alcohol to benzaldehyde. All these catalysts were found to be active and very selective (>97%) to the desired product (benzaldehyde). However, MgO prepared via the thermal decomposition of magnesium oxalate displayed the highest activity among all the magnesium oxide supports tested. Attempts were made to unravel the reasons for the deactivation of these catalysts using different characterisation techniques namely in situ XRD, XPS, ICP-MS, TEM, and TGA-MS. From the data obtained, it is clear that MgO undergoes phase changes from MgO to Mg(OH)2 and MgCO3 during catalyst preparation as well as during the catalytic reaction. Besides phase changes, strong adsorption of reactants and products on the catalyst surface, during the reaction, were also observed and washing the catalyst with organic solvents did not completely remove them. The phase change and catalyst poisoning were reversed through high temperature heat treatments. However, these processes led to the sintering of the metal nanoparticles. Moreover, substantial leaching of the support material (MgO) was also observed during the reaction. These latter two processes led to the irreversible deactivation of AuPd nanoparticles supported on MgO catalyst during the solvent-free selective aerobic oxidation of alcohols. Among the three different MgO supports studied in this article, an inverse correlation between the catalytic activity and Mg leaching has been observed. This article reports a deeper understanding of the mode of deactivation observed in metal nanoparticles supported on MgO during liquid phase reactions.

Walnut shell ash as a sustainable material for compounding with bromobutyl rubber for tire inner liner applications

“…For commercial MgO, the first weight loss of 6.3% at 124 C is attributed to removal of moisture and the second weight loss of 12.2% at 348 C is possibly attributed to release of CO 2 . It has been previously reported that water is lost between 250 C and 400 C and CO 2 removal occurs between 325 C and 500 C. [31,32] The endotherm peaks for commercial MgO at 167.7 C and enthalpy change (ΔH) of 34.4 J/g are attributed to removal of moisture content. Thermal decomposition of WNS ash up to 150 C with weight loss of 4.6% are probably attributed to the removal of moisture and weight loss of 12.9% at 747 C is possibly attributed to melting transition temperature of potassium oxide.…”

Three-dimensional N-doped graphene aerogel-supported Pd nanoparticles as efficient catalysts for solvent-free oxidation of benzyl alcohol

“…31,34 This catalyst has been applied in the selective oxidation reactions of benzyl alcohol in the liquid phase via an ideal green process using molecular oxygen as an oxidant; moreover, no solvent or additives have been used in this reaction, which is an important alcohol oxidation reaction in industries due to the demand for benzaldehyde that is used as an intermediate in the production of ne chemicals, fragrances and avouring additives. [35][36][37][38] This material has not only the advantages of two-dimensional graphene materials, but also other unique characteristics such as loose porosity, low density, large surface-to-volume ratio, strong mechanical properties and good electrical conductivity; moreover, NMP is similar to a stent, further extending the distance between graphene sheets such that the three-dimensional network structure has a larger surface area. The large specic surface area and more active sites due to N doping can effectively avoid the agglomeration of palladium nanoparticles, improve the dispersion of the nanoparticles, and thereby synchronously provide high selectivity and conversion.…”

Pd Nanoparticles Supported on Amine-Functionalized MgAl Layered Double Hydroxides for Solvent-Free Aerobic Oxidation of Benzyl Alcohol

“…The binding energies of Pd 3d5/2 (3d3/2) were found to be 336.2 eV (341.5 eV) for Pd/LDH and Pd/LDH-NS. In contrast, a lower binding energy of 335.8 eV (341.1 eV) was observed on Pd/NH2-LDH-NS, which is indicative of electron transfer from N to Pd [33][34][35]. Table 2 lists the catalytic results of the various Pd catalysts in solvent-free selective oxidation of benzyl alcohol to benzaldehyde with molecular oxygen at atmospheric pressure without basic additives.…”