Role of phosphorus on activated carbons used as catalytic support in steam reforming of pyrolysis liquids

Abstract

Hydrogen production from steam reforming (SR) of the liquids resulting from biomass waste pyrolysis with nickel catalysts is a sustainable alternative for decarbonization. Chemical activation with H3PO4 provide activated carbons (ACs) with high surface area and porosity development, improved surface oxidation/gasification resistance and acid character due to the presence of stable surface phosphorus groups. In addition, they can be prepared from the same biomass waste making them sustainable supports for steam reforming Ni catalysts. However, little is known about the role of surface P groups on the activity of nickel. In this work ACs, with different amounts of P, have been used as support for steam reforming Ni catalysts in order to study the effect of P on the catalytic activity and stability. Pistachio shell (PS), a non-edible agroforestry waste, has been used as feedstock for both the preparation of the activated carbons (ACs) and the pyrolysis liquids. P-containing AC was obtained by chemical activation of PS with 3:1 acid to precursor mass ratio and activation temperature of 500 ºC (PS3P sample). The amount of surface P in PS3P was partially decreased by hydrogen treatment at 600 ºC for 4 h (PSLP sample). P-free AC was also prepared by CO2 physical activation of PS at 800 ºC for 3 h (PSG sample). 10 % wt. Ni nominal loading were supported onto the ACs by the incipient wetness impregnation method with Ni(NO3)2·6H2O and thermal annealing in N2 atmosphere at 700 ºC for 2 h. The resulting catalysts have been evaluated on SR of a mixture of oxygenated hydrocarbons (ethanol, acetone and acetic acid) usually found in pyrolysis liquids. Each of them was fed with a 0.75 % volume concentration, while the steam to carbon ratio was set on the stoichiometric value. The reaction was carried out in a fixed bed tubular reactor at a temperature ranging from 500 to 800 °C and using a space time of 50 gcat·s·mmol-1.