Abstract
Hydrogenations and hydrodeoxygenations represent two of the most important reactions in the production of both bulk and fine chemicals. Despite the wide and long use of metal-based catalysts for this reaction, there is still some uncertainty with respect to the properties governing the catalyst activity. Using the hydrogenation of benzaldehyde as a model reaction, in this paper, we disclose the dominant parameters determining catalyst activity of Pd nanoparticles supported on a carbonaceous material (carbon nanoplates, GNP). In particular, several operating parameters of the catalyst synthesis were varied in order to obtain materials with differences in such physico-chemical properties as nanoparticle size, Pd oxidation state and Pd surface exposure. A linear correlation between catalyst activity and the amount of surface Pd(0) atoms was found; this dependence, maintained after catalyst recycling, pointed out the nature of the active site of the Pd/GNP catalyst represented by exposed Pd(0) species.
Highlights
The ultimate goal in heterogeneous catalysis is the accurate design of a catalyst that drives the reaction to the desired products
From a catalytic point of view, many studies showed that the Pd NPs’ sizes can largely influence the catalyst activity during the reduction of nitro compounds [16,17], the electrocatalytic reduction of CO2 [18] and the hydrogenation of allyl alcohol [19], but some studies highlighted the importance of the initial oxidation state of the active metal
(vinyl alcohol) (PVA) was used as stabilizer; the Poly(vinyl alcohol) (PVA)/metal weight ratio was changed from 0.2 to 1.0, while two catalysts were prepared using either pure ethanol (EtOH) or a mixture of water and ethanol (1:1 vol/vol) as solvent instead of pure water used for the other synthesis
Summary
The ultimate goal in heterogeneous catalysis is the accurate design of a catalyst that drives the reaction to the desired products In this sense, researchers are deeply studying the properties of catalysts to reach correlations between the activity of a catalyst and its features [1]. The key feature of preparation by sol-immobilization is the use of capping agents [8,9,10,11], which prevent the agglomeration of NPs during both the their synthesis and immobilization steps, providing good metal dispersion on the support. The effect of the Pd particle size and oxidation state on the activity and selectivity during muconic acid hydrogenation was evaluated [23], and it was shown that the increasing of Pd0 contents improves the catalyst activity towards adipic acid formation
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