Hollow nitrogen- and boron-doped carbon submicrospheres with a porous shell. Preparation and application as supports for hydrodechlorination catalysts

Abstract

Nitrogen- or boron-doped carbon submicrospheres with a hollow core and a porous shell were prepared via a template method and tested as supports for Pd/C catalysts. The carbon precursor was a phenol-formaldehyde resin that was generated into a silica template using pyridine, 1,10-phenantroline, and sodium tetraphenylborate as doping agents. The nitrogen and boron atomic percentages in doped carbon reached 0.5–3.6 and 0.03–0.67, respectively. High specific areas of up to 1846 m2/g with an important contribution of mesopores were achieved. The prepared Pd catalysts (1% w) exhibited unique features due to the morphology, porous structure, and doping of the support. The active phase was well-dispersed as nanoparticles with narrow size distribution (<10 nm) in an outer shell with a thickness of 77–124 nm. The short diffusion path needed for reactants and the well-developed network of mesopores of the shell contributed to diminish mass-transfer constraints. The catalysts showed remarkable activity (50–76 mmol/g·min) in the batch aqueous-phase hydrodechlorination of 4-chlorophenol at 30 °C and 1 atm, with higher values for the catalysts based on doped supports. Doping also promoted the selectivity toward hydrogenation products, particularly in the case of nitrogen-doped supports. The effect of support doping was more important at the 60 °C reaction temperature. The activity was maintained upon reuse, but the selectivity to hydrogenation products decreased.