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A new method for preparing colloidal suspensions of R-zirconium phosphate (R-ZrP), based on the use of a phase swelled with n-propylamine vapors, is described and applied to the synthesis of new chromiapillared materials. The colloidal phase was obtained by contacting the n-propylamine intercalate with a dilute aqueous solution of acetic acid. For comparison, a conventional procedure of colloidization, based on the addition of a n-propylamine aqueous solution to the pure phosphate, was also employed. The intercalation of polyhydroxoacetato Cr III clusters was accomplished by refluxing chromium acetate solutions with each colloidal phosphate suspension. The new method gave rise to chromium oligomer intercalates with higher basal expansions, and moreover, larger oligomeric species seemed to be intercalated with a high chromium concentration in solution. Two series of chromia-pillared materials were obtained by calcination of the intercalated precursors at 673 K under N2. In both series, the acidity, as determined by TPD-NH3 and pyridine adsorption, increased with chromium content. The chromia-pillared materials prepared by the new method displayed a high porosity and catalytic activity for the decomposition of isopropyl alcohol. Under the experimental conditions used, all catalysts behaved exclusively as dehydrating catalysts.

Two series of porous chromia-pillared α-zirconium phosphate materials, prepared using two different methods of colloidization of the initial phase and with variable chromium contents (CrZrP-Xa and CrZrP-Xb) have been tested in the oxidative and nonoxidative dehydrogenation of propane in a flow reactor at atmospheric pressure. All catalysts are highly selective to propene under nonoxidative conditions at 823 K. In both series of catalysts, the initial activity increases with the chromium content, but generally CrZrP-Xb catalysts are more active than those of series CrZrP-Xa, which is in good agreement with their higher chromium contents and greater dispersions. In all cases, deactivation was detected due to coke formed from undesired reactions. When the reactions were carried out under oxidative conditions at 673 K, the activities were enhanced and the observed deactivation was minimum. The activities found vary between 0.47 and 1.31 μmol of propene g-1 s-1 and are maintained after 200 min of reaction. These activity values were also related to the chromium content, being slightly higher for CrZrP-Xb materials. A parallel study to evaluate the influence of acidity in the obtained results has been carried out. The activities found of these catalysts seem to be related to the presence of Cr(III) centers with vacancies in their coordination sphere. These vacancies, in nonoxidative conditions, can activate the reactive molecules originating propene and hydrogen. On the other hand, in an oxidative atmosphere, Cr(III) species can activate oxygen molecules, through an electronic transference process, yielding propene and water.

Chromia-pillared α-zirconium phosphate materials have been prepared by two different methods:  series a, using as precursor a preswelled phosphate prepared by neutralization up to 70% of the exchange capacity with n-propylamine in aqueous solution, and series b, preswelling the phosphate with n-propylamine vapors up to saturation. Sulfidation of the pillared materials with a H2S mixture at 673 K did not result in the formation of isolated chromium sulfide phases but in partial sulfided chromium-oxide-pillared phosphate. The catalysts have been characterized by nitrogen adsorption, X-ray photoelectron spectroscopy (XPS), and oxygen chemisorption. After sulfidation, the modification of textural parameters observed was negligible and slightly different in both series, probably due to higher sulfidation in the pillars of series b. The higher dispersion of chromia in materials of series b detected by XPS was corroborated by the oxygen chemisorption study of the sulfided-pillared materials. Sulfur is found to be present as S2- species. The sulfided catalysts exhibited a high activity and stability for thiophene hydrodesulfurization (HDS), particularly the sulfide−CrZrP-3b material, which, despite its deactivation, after 6 h on stream is very active. However, the oxidic pillars showed an unusual activity, similar to those of sulfided materials. So, the chromia-pillared catalysts, above all those of series b, do not need the initial sulfidation to achieve a considerable activity. The optimal sulfidation temperature and reaction temperature was 673 K. The thiophene hydrodesulfurization exclusively gives rise to the formation of butane and butenes. The constants for hydrogenation of butenes to n-butane have also been calculated.

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