A heat‐resisting acid catalyst: Thermal stability and acidity of a thin silica layer on alumina calcined at 1493 K

Abstract

The chemical vapor deposition of a thin layer of silica on alumina is shown to improve the thermal stability of alumina with respect to sintering and to reduce the loss of surface area of alumina during heating. Benzaldehyde-ammonia titration showed that samples with high stability were almost completely covered by silica. These observations suggest that an ultrathin silica layer, probably a monolayer, thermally stabilizes the surface. Brsnsted acidity was observed even after calcination at 1493 K: it was initially diminished by this calcination, but readily recovered on exposure to a humid atmosphere, whereas conventional solid-acid catalysts are irreversibly deactivated by complete sintering.

Behaviour of Amorphous Aluminosilicates towards Ageing by High‐Temperature Steaming

“…The porosity of alumina is maintained, but the distribution of silicon species inside the pores is modified. Other studies had even demonstrated the beneficial effect of silica‐coated alumina, in which surface silica species prevent the alumina core from sintering by limiting the diffusion of aluminium species,7, 8, 22, 23 especially at a moderate silica loading (between 10 and 20 wt % silica9, 24). The NMR spectroscopy results (Figure 4) confirm that neither the structure of the deposit nor that of the support has changed substantially.…”

Controlling Surface Composition and Zeta Potential of Chemical Vapor Synthesized Alumina‐Silica Nanoparticles

“…Due to the vanishing differences of the half life of the precursors at these high temperatures (1400 C) a homogeneous distribution of the elements in the particles seems likely. A rearrangement (due to calcination) into separate alumina and silica phases as reported in the literature [15] seems unlikely because of the very short residence time (110 ms) of the particles in the hot zone. Figure 3 shows the X-ray diffractogram of the transitional Al 2 O 3 and of the powders that were produced with premixed precursor flows.…”

Dealkylation of alkyl polycyclic aromatic hydrocarbon over silica monolayer solid acid catalyst

“…The Si-O-Al bond was formed during the CVD process, and the remained -OCH3 group was removed by calcination of the sample at >673 K, as observed by in-situ IR experiments [59] and weight monitoring [62]. The calcination at 673-1173 K gives principally stable properties where the Si concentration was 8-12 nm -2 [60]. Based on these facts, we selected tetramethoxysilane as the precursor of silica, 593 K as the CVD temperature and 673 K as the calcination temperature in this study.…”

“…Chemical vapor deposition (CVD) of Si precursor on the surfaces of oxides with weakly or moderate basic nature such as alumina and zirconia have been tested to form new catalysts or catalyst supports by several authors [49][50][51][52][53][54][55][56][57][58]. Among them, the silica layer on alumina has been found to have catalytic activity for Brønsted acid-catalyzed reactions [50,59 ] and very high thermal stability [54,57,60]. The influences of precursor of silica, CVD temperature and calculation temperature have been studied extensively as follows.…”