Phosphoric acid intercalated Mg-Al hydrotalcite-like compounds for catalytic carboxylation reaction of methanol in a continuous system

摘要

Mg-Al-hydrotalcite-like catalysts (HTlcs) with different amount of P/Mg molar ratio were prepared via co-precipitation method and calcined at 450 degrees C. The synthesized catalysts were tested in the direct-carboxylation reaction of methanol in gas phase in a continuous system such as chemical route for CO2 valorization. Activities around 2% with total selectivity towards the dimethyl carbonate (DMC) was obtained at moderate temperatures (150 degrees C) with both Mg/Al mixed oxides (HTO) and phosphated Mg/Al mixed oxides (HTc-9c). Even though the conversion increased until 16% at higher temperatures (200 degrees C), the selectivity with both catalysts (HTO and HTc-9c) decreased due to the decomposition of DMC to dimethyl ether (DME). Nevertheless, the catalyst with P showed less DMC decomposition and a higher selectivity towards the desired product. This is explained by the presence of orthophosphate species bonded to the Al3+ metals of the HTs (O-P(OAl)(3)) which give to the catalyst a higher structural stability and specific acid properties.