Vanadium-sludge from a drinking water treatment plant as catalysts for CO2-assisted ODH of ethylbenzene: Relationship between heterogeneous catalysis and electrochemistry

Sludge derived from a drinking water treatment plant has been used as a support for vanadium to be used as catalyst for the oxidative dehydrogenation (ODH) of ethylbenzene using CO₂ as a mild oxidizing agent. The valorization of this sludge is particularly attractive, as it is abundantly generated during water treatment processes and constitutes a widely available residual material. The sludge was characterized by physicochemical and electrochemical techniques, which revealed that the optimal vanadium concentration, ca. 4 wt%, corresponds to the highest loading employed without the formation of unselective crystalline V 2 O 5 . As a novelty, the catalytic performance of these V/sludge catalysts has been correlated with their electrochemical properties, showing that high activity is obtained when the density of acceptors is high and the resistance to the charge transfer of the outer layer is low. Unfortunately, due to carbon deposition and slight reduction of V 5 + to V 4+ , a minor deactivation occurs after 8 h. Finally, we want to mention that consistent yields to styrene of 75% can be obtained with a catalyst with intermediate V-loading (ca. 4 wt%) in non-optimized reaction conditions. • High yield to styrene of 79% in the ODH-CO 2 of ethylbenzene. • Relationship between the electrochemical behavior and catalytic performance. • Vanadium on sludge performance surpasses V/metal oxide supports.