Possible mechanism of structural incorporation of Al into diatomite during the deposition process I. Via a condensation reaction of hydroxyl groups

Enhancement of diatomite solid acidity by Al incorporation, as evaluated by the catalytic effects on the thermal decomposition of 12-aminolauric acid

“…This band for Dt/Al 350 -NH 3 is hardly distinguished and is not observed in the curve of Dt/Al 500 -NH 3 . The weakening and disappearance of this NH 3 -desorption band for Al-incorporated diatomite is attributed to the decrease in number of diatomite Si-OHs, which react with Al 13 hydroxyl groups, as revealed by 29 Si MAS NMR spectra (see our previous report [24]). …”

“…In the case of samples heated at ≥350 • C, the number of B acid sites decreased because of the dehydroxylation of Al-OHs of Al 13 , whereas unsaturated Al 3+ ions formed and the number of L acid sites (Al-) consequently increased [24,32]. L acid sites were predominant when Al was incorporated into the structure of diatomite and heated at 500 • C, as displayed in the FTIR spectra in our previous study [24]. Therefore, the 255 • C band, which is the predominant band in the TPD curve of Dt/Al 500 -NH 3 , is attributed to the desorption band of NH 3 bound to L acid sites.…”

“…These two bands are assigned to the NH 3 desorption of B (Al-OHs) and L (unsaturated Al 3+ ions, which are denoted here as Al-) acid sites from Al 13 [24,31]. In the case of samples heated at ≥350 • C, the number of B acid sites decreased because of the dehydroxylation of Al-OHs of Al 13 , whereas unsaturated Al 3+ ions formed and the number of L acid sites (Al-) consequently increased [24,32]. L acid sites were predominant when Al was incorporated into the structure of diatomite and heated at 500 • C, as displayed in the FTIR spectra in our previous study [24].…”

“…The structure, morphology and macroporosity of the diatomite before and after the Al incorporation are described in our previous report [24].…”

“…In our recent study [24], hydroxyl aluminium polymer (tridecameric aluminium polymer, abbreviated to Al 13 ) was incorporated into the structure of diatomite via a condensation reaction to investigate the possible mechanism of its incorporation. The solid acidity of diatomite markedly increased, and L acid sites appeared after the Al incorporation, as investigated using Fourier transform infrared (FTIR) spectroscopy.…”