Bio-derived butadiene from cross-metathesis over silanol rich WO3 catalysts obtained from copper phyllosilicate†

Bio-butadiene can be produced from cross-metathesis of bioethanol-derived acetylene/ethylene over supported WO₃ on silanol-rich silica prepared with Cu-leached copper phyllosilicate (CuPS). 20CuPS and 30CuPS were preliminarily reduced before Cu-leaching under an acidic solution (1 M HCl). Compared with fumed SiO₂, ²⁹Si CPMAS NMR spectroscopy showed an increase in surface silanols, particularly the isolated silanols (Q₃), from removing Cu²⁺ octahedral sites (Cu²⁺(OSi)₆) encapsulated within tetrahedral silica layers of CuPS. The surface silanols in fumed SiO₂, 20CuPS-Le, and 30CuPS-Le adequately accommodate single-site and polymeric WO₃ species, leading to a similar 1,3-butadiene production rate (∼4.7 mmol h⁻¹ g_cat) at 5 wt% loading. Only 30CuPS-Le sufficiently provides the exposed silanols to disperse 8 wt% WO₃ loading without bulk WO₃ formation. The cross-metathesis activity depends on the relative amounts of exposed silanols. Accordingly, the steady 1,3-butadiene production was obtained in the order of 8WO₃/30CuPS-Le (6.3 mmol h⁻¹ g_cat) > 8WO₃/20CuPS-Le (5.1 mmol h⁻¹ g_cat) > 8WO₃/SiO₂ (2.5 mmol h⁻¹ g_cat).