Mixed oxide catalysts were studied for a model acylation - m-toluic acid reacting with diethylamine to N, N-diethyl-3-methylbenzamide (DEET) - and compared to standard homogeneous catalysts such as titanium chelates. More acidic catalysts such as hydroxyapatites and supported 12-tungstophosphates were active, stable in a gas phase, and selective with stoichiometric feeds. Optimal results (long-term MTA conversion of 78 +/- 6%, DEET selectivity of 86 +/- 3% at WHSV = 3-9 h(-1), no deactivation over 100 h) were obtained with a supported 12-tungstophosphate at 573 K, 0.1 MPa.