Amorphous AlPO4-Al2O3 (5-25 wt% Al2O3, APAl-A) systems were selective
catalysts for the N-alkylation of aniline with methanol. The methylati
on reaction (that was carried out in a continuous down-flow reactor op
erating at atmospheric pressure, 523 K and aniline feed rates over 3 x
10(-6) mol s(-1)) is a pseudo-first order process with respect to ani
line concentration, taking place through consecutive formation of N-me
thyl and NN-dimethylanilines. Also, there is always more N-methylanili
ne (NMA) than N,N-dimethylaniline (NNDMA). Increasing reaction tempera
ture enhances the selectivity of NNDMA. AlPO4 and Al2O3 are slightly a
ctive, but AlPO4-Al2O3 catalysts exhibit significantly higher activity
(an order of magnitude more active) and, besides, there is a slight i
ncrease in activity on increasing Al2O3 loading up to 15 wt%, thereby
showing that APAl-A catalysts are suitable for selective obtaining N-a
lkylation products. The effect of surface acidity on aniline alkylatio
n activity is discussed. Strong acid sites are not required for the N-
methylation of aniline, whereas, weak to moderate acid sites seem to b
e responsible for this reaction. Furthermore, there is no catalyst dea
ctivation by coke deposition, whereas, the addition of pyridine or 2,6
-dimethylpyridine deactivate the catalyst. (C) 1998 Elsevier Science B
.V.