Abstract
Biochars are attractive materials for carbon catalysts since their carbon content and surface area are relatively high and minerals present in biochar can act as active sites for catalytic reactions. In this study, biochars from the fast pyrolysis of birch, pine, and unbarked willow were activated and acid washed. These materials were tested as catalysts for a post-treatment of pine wood pyrolysis vapors, aiming at stabilizing the vapors before their condensation. All the unmodified biochars had high content of minerals, those being highest in willow due to the bark. After the activation treatments, the surface areas and pore volumes of all biochars significantly increased. All studied biochars and activated carbon catalysts reduced the oxygen content of the pyrolysis degradation products. This effect was more pronounced for compounds derived from polysaccharides vs. lignin. The most promising catalyst for vapor upgrading was unwashed activated carbon from willow, having high surface areas and pore volumes together with high mineral contents. These properties together promoted the high conversion of polysaccharide-derived products (anhydrosugars, acids, and pyrans) into CO2. Release of highly oxidized degradation products may indicate that reductive stabilization takes place via hydrogen migration from the polysaccharide-derivatives to lignin derivatives, mediated by the carbon catalyst.
Highlights
Carbon materials are widely used as catalyst supports or as heterogeneous catalysts
The unwashed willow biochar and steam activated willow biochar were chemically activated by sulfonation and analyzed for their physical and chemical characteristics, to the unsulfonated biochars
Show high carbon contents for the biochars, which increased further due to the high temperature steam activation treatment
Summary
Carbon materials are widely used as catalyst supports or as heterogeneous catalysts. They have many good properties required for a catalyst. They have very high surface areas reaching thousands of m2 /g [1], enabling a high density of active sites and high activity. Typically acid or basic groups are created on the carbon surface. Activation treatments can be divided into physical and chemical treatments, and they typically increase the surface area and porosity of the material. Acidic or basic surface groups can act themselves as active sites (heterogeneous acid/base catalysis) or they can act as anchoring sites if an active metal is deposited on the carbon surface [2]
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