| abstract |
Provided is a solid phosphoric acid catalyst which, when gas-phase synthesizing trioxane from formaldehyde, obtains trioxane at a high yield and at a high selection rate by markedly suppressing side reactions, and which reduces the adhesion of organic matter to the catalyst surface, and achieves a stable and long-term catalyst reaction. This solid phosphoric acid catalyst contains silicon phosphate oxide (SPO) obtained by sintering at a temperature of at least 200°C a carrier material to which a phosphoric acid component has been added, and the total quantity of acid does not exceed 5mmol per 1g of solid phosphoric acid catalyst when calculated as acid quantity determined by NH 3 -TPD measurement. The average specific surface area of the solid phosphoric acid catalyst preferably does not exceed 20m 2 /g, the carrier is preferably selected from porous silica, aluminum hydrosilicate, or diatomaceous earth, and the SPO is preferably a dehydrated composite compound of the aforementioned carrier and a phosphoric acid selected from orthophosphoric acid, pyrrophosphoric acid or polyphosphoric acid, or a precursor thereof. |