Abstract
The polymorphism of tungsten carbide (W (x) C) and the challenge of selectively synthesizing pure phases have impeded a precise understanding of catalytic structure-property relationships. This study establishes a framework for phase-selective synthesis of W (x) C through controlling carburization kinetics. By maintaining particle sizes below 10 nm, β-W(2)C is selectively synthesized using gaseous carbon precursors (CH(4)/H(2)) via temperature-programmed carburization (TPC). Our findings reveal that W(2)C stabilization is predominantly dictated by particle size and carburization kinetics rather than support interactions, providing a tunable approach to synthesize tungsten carbide catalysts. We elucidate the mechanistic pathway of WO (x) carburization, demonstrating that CH(4) activation occurs at mild temperatures via lattice oxygen. Our reactor studies establish ex situ synthesized β-W(2)C as an active and stable catalyst for the reverse water-gas shift (RWGS) reaction. However, the need for passivation and reduction pretreatment leads to a complex surface structure with diminished intrinsic activity. In contrast, our in situ synthesis protocol for β-W(2)C eliminates the need for passivation and exhibits increased CO STY during RWGS, illustrating the intrinsically higher activity compared to metallic W, WC(1-x) (0.5 < x < 1), and stoichiometric WC.