Abstract
Supported 12-molybdosilicic acid catalysts were prepared by impregnating various supports, SiO2, SiO2• Al2O3-L, SiO2•Al2O3-H, Al2O3, or MgO with a solution of the acid, and the activities and selectivities of the catalysts were measured to compare the results obtained with the pore size distributions and surface basicities of the catalyst supports. The use of SiO2 with micropores resulted in an increased formation of isobutene dimers and hence caused to depress the selectivity of the catalyst at high reaction temperatures (Figs. 1, 2). Thus, the use of SiO2 with pores greater than 100Å was recommended for preparing a catalyst for selective synthesis of MTBE. Furthermore, the order of effectiveness of the catalyst supports used was found to be as follows: SiO2>SiO2•Al2O3-L>SiO2•Al2O3-H> Al2O3_??_MgO=0 (Fig. 3). This result was reasonably explained in terms the surface basicity of the catalyst support (Figs. 5, 6). Namely, the decomposition of 12-molybdosilicic acid due to the reaction of the acid with the surface base was considered to depress the activity of the catalyst.
The above mentioned view of the role of the catalyst supports was justified by high activity of two catalysts, i. e., 12-molybdosilicic acid impregnated on carbon black support (Fig. 1) and the other prepared by impregnating Al2O3 with an ethanol solution of 12-molybdosilicic acid (Fig. 7).
