Acidity-reactivity relationships in catalytic esterification over ammonium sulfate-derived sulfated zirconia

New insight was gained into the acidity-reactivity relationships of sulfated zirconia (SZ) catalysts prepared via (NH4)2SO4 impregnation of Zr(OH)4 for propanoic acid esterification with methanol. A family of systematically related SZs was characterized by bulk and surface analyses including XRD, XPS, TGA-MS, N2 porosimetry, temperature-programmed propylamine decomposition, and FTIR of adsorbed pyridine, as well as methylbutynol (MBOH) as a reactive probe molecule. Increasing surface sulfation induces a transition from amphoteric character for the parent zirconia and low S loadings <1.7 wt %, evidenced by MBOH conversion to 3-hydroxy-3-methyl-2-butanone, methylbutyne and acetone, with higher S loadings resulting in strong Brønsted-Lewis acid pairs upon completion of the sulfate monolayer, which favored MBOH conversion to prenal. Catalytic activity for propanoic acid esterification directly correlated with acid strength determined from propylamine decomposition, coincident with the formation of Brønsted-Lewis acid pairs identified by MBOH reactive titration. Monodispersed bisulfate species are likely responsible for superacidity at intermediate sulfur loadings

Low-Temperature IR Spectroscopy of CO Adsorption on Calcined Supported CeO: Probing Adsorbed Species and Adsorbing Sites

Carbon monoxide adsorption on ceria dispersed on silica (CeSi) and alumina (CeAl) at 300–80 K was observed by in-situ IR spectroscopy. For control purposes, CO adsorption was also observed on unsupported CeO 2 and the individual support materials (SiO 2 and Al 2 O 3 ). The adsorbents were prepared ex situ by heating at 770 K (3 h) in air, and pretreated in situ by heating at 720 K (1 h) in oxygen and then in vacuum. The results, as disclosed by v(OH) (3900–3300 cm −1 ) and v(CO) (2250–2050 cm −1 ) spectra taken before and after CO adsorption, reveal that CO adsorbs on all of the test adsorbents at temperatures < 300 K only. The resulting adsorbed species include CO coordinated to Lewis acid sites (on all of the adsorbents, but not SiO 2 ), hydrogen-bonded CO (on all of the adsorbents, but not CeO 2 ) and CO bound to electron-rich defect sites (only on unsupported CeO 2 ). It is concluded that the dispersion of ceria, particularly on alumina, is associated with a considerable development of the Lewis acidity of Ce 4+ sites

The Influence of Phosphate and Sulphate Ions on the Surface Texture of Alumina

The impact of the addition of phosphate and sulphate salts to aluminas, viz. γ-alumina and dried alumina gel, on their surface textures is described. This has been achieved through an analysis of nitrogen adsorption data for structurally characterised test samples. Modification through impregnation by phosphate and sulphate salts did not result in detectable bulk changes, the structure remaining very similar to that of γ-alumina in all cases. However, as far as the texture was concerned, the addition of both phosphate and sulphate salts resulted in a ca. 15% reduction in the S BET value for γ-alumina due to changes in the porosity. Modified alumina gel exhibited a higher surface area than either pure or modified γ-alumina. Thus, for the purposes of obtaining catalytically important acidified aluminas with higher surface areas, it is recommended that phosphates or sulphates be added to the parent alumina gel prior to calcination

Nitrogen Sorptiometric Study of Phosphation and Dispersion of Lanthanum(III) Oxide on Alumina Catalysts

Alumina-supported lanthanum(III) oxide catalysts at loadings varying in the range 3–30 wt% La 2 O 3 were prepared by wet impregnation and calcination at 920 K for 2 h. An analogous series of catalysts were phosphated by impregnation with up to 6 wt% PO 4 3– from aqueous solutions of (NH 4 )H 2 PO 4 and then calcined similarly. The catalysts thus obtained were characterized by X-ray diffractometry, infrared spectroscopy and nitrogen sorptiometry at 77 K. The adsorption data were analyzed by the BET method and the t-method. The results suggested that lanthanum(III) oxide loadings up to 30 wt% exist as high-dispersion two- and three-dimensional structures on the surface of alumina that are not XRD-detectable (particle size < 2 nm). Strong interactions not only at the liquid/solid interface established during impregnation, but also at the solid/solid interface established during drying and/or calcination, are suggested to be important events in the dispersion mechanism. Phosphation led to the improvement of the two-dimensional lanthanum(III) oxide dispersion (probably in monolayers) rather than the three-dimensional one, most likely through direct bonding of the phosphate groups to exposed La 3+ sites. It is inferred that nitrogen adsorption data can provide valuable qualitative information on the dispersion of supported oxide materials