Potential application of zirconium molybdate as a novel catalyst for the selective dehydrogenation of methanol to anhydrous formaldehyde

The non-oxidative dehydrogenation of methanol is considered a promising method for producing formaldehyde (FA), where the resulting anhydrous formaldehyde is perfect for the use in the subsequent generation of oxygenated synthetic fuels. In the current investigation, a series of Zr(MoO₄)₂ nanoaggregates, as a novel solid acid catalyst, were hydrothermally fabricated at different temperatures in the presence of triethylamine (TEA) as a surfactant. The original and calcined catalysts were characterized by TGA, DSC, XRD, FT-IR, XPS, HR-TEM, acidity and nitrogen sorption. Analyses revealed that the addition of TEA to the preparation procedures significantly enhanced the textural, acidic, and the catalytic performance of these catalysts. Acidity measurements reflected that the surface of these catalysts possessed Brønsted type of acidic sites of weak and intermediate strength. Catalytic activity results demonstrated that, Zr(MoO₄)₂ catalyst with Zr: TEA molar ratio of 1:1 (Z₁T₁) annealed at 400°C exhibited the maximum methanol conversion of 99% and 95% selectivity to formaldehyde at reaction temperature of 325°C. The remarkable catalytic performance was well correlated to the variation in acidity of the catalyst. This catalyst offered a long-term stability towards the production of formaldehyde for a period of time of 160 h with the same activity and selectivity. Also, this catalyst could be re-used for five time giving almost the same performance. The reason for this extreme catalytic activity and selectivity towards formaldehyde synthesis is the presence of weak and moderate strengthened Brønsted acid sites. In light of this, this work has produced an active, stable, and selective catalyst for the conversion of methanol to formaldehyde that is competitive with the most effective conventional and recently discovered catalysts.