Co-pyrolysis of leather shaving waste and rice husk for hybrid palladium-supported biochar catalysts in hydrogenation reactions

The co-pyrolysis of tanned leather shaving waste (LS), a byproduct of the tanning industry, and rice husk (RH), an abundant agrifood residue, was performed to produce a hybrid activated biochar (ARL) to be used as support in the preparation of a Pd-based catalyst (Pd/ARL). The catalytic performance of Pd/ARL was compared with Pd/biochar catalysts derived from the pyrolysis of the individual feedstocks (Pd/ARH from rice husk and Pd/ALS from leather shaving) in the hydrogenation of benzaldehyde. Pd/ARH and Pd/ARL exhibited significantly higher initial activity, with turnover frequencies greater than Pd/ALS (1.41 s⁻¹ and 0.58 s⁻¹ vs. 0.09 s⁻¹, respectively). However, Pd/ALS and Pd/ARL demonstrated superior selectivity toward the desired product, benzyl alcohol (92 and 94 % for the former and later cases, respectively, vs. 78 % for Pd/ARH), effectively suppressing side reactions such as benzaldehyde acetalization with ethanol. Chemical and physical characterization of the biochars and catalysts revealed that Pd/ARL benefits from the synergistic properties of both feedstocks, including enhanced metal anchoring, high dispersion, and unique oxidation states. These factors contributed to the best overall catalytic performance, increasing the yield of desired products by up to 96 %. This research disclosed a novel strategy for the fabrication of cost-effective catalytic supports from waste materials aimed at modulating the hydrogenation reactions selectivity.