Effect of Si/Al ratio, calcination temperature and post-synthesis phosphorus modification on the textural, structural, acidic, and catalytic properties of amorphous silica-alumina prepared by deposition methods

Amorphous silica-aluminas (ASAs) were prepared by Si- (DSi) and Al- (DAl) deposition methods with subsequent post-synthesis phosphorus modification (ASAs/P). DAl catalysts with varying bulk Si/Al molar ratio produced high densities and strong-strength Brønsted (BASs) and Lewis (LASs) acid sites, whereas DSi had lower densities and strengths. The DAl(29-6) and DAl(48-8) catalysts achieved complete methanol conversion, contrasting with the reference catalyst γ-alumina, in alcohol dehydration. A detriment of the catalytic activity (1-10%) was observed with increasing calcination temperature from 600 °C to 800 °C for DSi and DAl catalysts. This decrease stemmed from the rise in weak-strength BASs and LASs densities at the expense of strong acid sites due to dehydroxylation. P-modification led to the formation of polyphosphates species (AlV-O-P and/or -O-P), comprising weak- and medium-strength BASs and LASs, resulting in very similar and homogenous activities (92.6-94.4%) of all ASAs/P catalysts. The findings revealed that medium-strength LASs and BASs, POH and LASs/P sites, synergistically and/or cooperatively participated in the mechanism for methanol dehydration. •Amorphous silica-aluminas were prepared by deposition routes and phosphorus modified.•ASAs calcined from 600°C to 800°C disimproved the acidic and catalytic properties.•Phosphorus-modified ASAs showed a similar and homogenous catalytic activity.•Synergy between Brønsted and Lewis acid sites for methanol dehydration on ASAs.•POH and LASs/P sites acted in the mechanism for dimethyl ether synthesis on ASAs/P.