Abstract
The influence of the surface chemical properties of the carbon support on the Pd dispersion, activity and stability of Pd(OH)2/C catalyst for the hydrogenolytic debenzylation of tetraacetyldibenzylhexaazaisowurtzitane (TADB) was studied in detail. The flowerlike nanosheet carbon material (NSC) was chosen as the pristine support, meanwhile chemical oxidation with nitric acid and physical calcination at 600 °C treatments were used to modify its surface properties, which were denoted as NSCox-2 (treated with 20 wt% HNO3) and NSC-600, respectively. The three carbon supports and the corresponding catalysts of Pd/NSC, Pd/NSC-600, and Pd/NSCox-2 were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), nitrogen sorption isotherm measurement (BET), powder X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectra (XPS), temperature-programmed desorption (TPD), temperature-programmed reduction (H2-TPR), thermogravimetric analysis (TG), and element analysis. The debenzylation activities of Pd/NSC, Pd/NSC-600, and Pd/NSCox-2, as well as the three catalysts after pre-reduction treatment were also evaluated. It was found that the activity and stability of the Pd(OH)2/C catalysts in the debenzylation reaction highly depended on the content of surface oxygen-containing groups of the carbon support.
Highlights
Carbon materials have been widely used as support to fabricate the heterogeneous catalysts due to its high stability, large tunable specific surface area, chemical inertness, easy tailorable surface chemical properties [1,2,3], especially for the precious metal catalysts
Palladium on carbon is an important class of catalyst, which can be used in several industrial chemical processes including hydrogenation, dehydrogenation, hydrogenolysis, hydro-dechlorination, nitroarenes reduction, and C–C coupling [4,5,6]
The wetting angles of the carbon supports were detected (Figure S4), which were in order of NSCox-2 < nanosheet carbon material (NSC) < NSC-600, showing a significant difference in hydrophilicity of the carbon supports due to the variety of concentrations of the surface oxygen-containing groups
Summary
Carbon materials have been widely used as support to fabricate the heterogeneous catalysts due to its high stability, large tunable specific surface area, chemical inertness, easy tailorable surface chemical properties [1,2,3], especially for the precious metal catalysts. An investigation of the catalytic performance of Pd-based hydrogenolytic debenzylation catalyst as a function of surface chemical properties of carbon support becomes desirable. The yield of product and the conversion of TADB over the re-used Pd/NSCox-2 were 75 and 83%, respectively (Table S1), which were significantly higher than the data of the re-used Pd/NSC (60 and 70%) and Pd/NSC-600 (10 and 15%), revealing the best stability of Pd/NSCox-2 in the hydrogenolytic debenzylation reaction All these results indicated that the chemical nature of the surface groups exerted a considerable influence on the interaction of the Pd species with the carbon carrier [3].
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