Tin oxide surfaces. Part 17.—An infrared and thermogravimetric analysis of the thermal dehydration of tin(IV) oxide gel

Abstract

The thermal dehydration of high-surface-area (ca. 180 m2 g-') tin(1v) oxide gel has been studied by thermogravimetric analysis and infrared spectroscopy in the temperature range 293-673 K. The thermogravimetricanalysis data show that two types of physisorbed water are present, one which is largely removed by evacuation at ambient temperature and a more strongly held type which is removed by evacuation at 373-423 K. Further mass loss occurring at higher temperatures is due to the condensation of hydroxyl groups on the surface of the oxide particles. The amount of physisorbed molecular water present on the freshly prepared gel corresponds to a ca. three-monolayer coverage, reducing to ca. 0.74 of a monolayer after evacuation at 295 K, and is totally removed after evacuation at 423 K. The surface concentration of hydroxyl groups is determined to be 19.8 nm-2 at 423-473 K, falling to 16.2 nmP2 at 573 K and 13.0 nm-2 at 673 K. Infrared spectra confirm that physisorbed molecular water [v (OH) 3800-2000 cm-I, &OH) 1640 cm-'1 is removed by 423 K. Isolated and hydrogen-bonded surface hydroxyl groups give rise to stretching modes at 3640 cm-l (sharp) and 3500 cm-' (very broad), respectively. Surface hydroxyl deformation bands are found at 870, 940, 1175 and 1245 cm-l. The bands at 870 and 950 cm-' are removed on evacuation by 473 and 523 K, respectively. The deformation bands at 1175 and 1245 cm-' which remain at 523 K are assigned to isolated surface hydroxyl groups. The band at 770 cm-', which increases in intensity during dehydration, is assigned to surface Sn-0-Sn linkages formed by the dehydroxylation process. The results are interpreted in terms of hydroxylated exposed [loo], [loll (both of which contain clusters of three hydroxyl groups attached to each surface tin atom) and [110] (which contains both isolated and geminal pairs of hydroxyl groups attached to surface tin atoms) crystal planes of the rutile structure, the former predominating.A knowledge of the chemical nature of the surface of tin(1v) oxide and its binary mixtures with other oxides such as Sn0,-

Synthesis of SnO2 nanopowders by a sol-gel process using propanol-isopropanol mixture

“…1, the FT-IR-ATR spectrum of the sol exhibits two new peaks in comparsion with n-propanol alcohol spectrum which indicate that C 3 H 7 OH has been hydrolyzed and has been reacted with SnCl 4 •4H 2 O to form Sn(OR) 4-x (OH) x complex. The peak at 1600 cm -1 corresponds to Sn-OR band [23] and the peak at 3500 cm -1 corresponds to Sn-OH band as well [24].…”

Combined X-ray Diffraction and Diffuse Reflectance Analysis of Nanocrystalline Mixed Sn(II) and Sn(IV) Oxide Powders

“…The persistence of water/OH groups associated with metal oxide materials at high temperatures has been noted in other studies. [47][48][49] Loss of water is attributed primarily to physisorbed molecular water until approximately 200 °C and above this temperature range to surface hydroxyl group condensation or chemisorbed water. 47,48 Rutile SnO2 is the thermodynamically stable phase at high temperature.…”

“…The broad absorption peak observed at ∼3450 cm -1 is due to OH stretching modes from molecular water and a weak band due to the water deformation mode at ∼1650 cm -1 . 48 The bands at ∼636 and 526 cm -1 for as-made material and at ∼656 and 526 cm -1 for sample heated at 200°C are assigned as Sn−O−Sn and Sn−O vibrations respectively, 3,63 and the latter is from Sn−OH. The peak positions of the material (a) at low temperatures are more similar to those of commercial nanocrystalline SnO2 powders than of commercial SnO.…”

Effect of Calcination Temperature on Structure and Properties of Sn–Nb2O5/α-Al2O3 Catalyst for Ethylene Oxide Hydration

“…5. Only one broad band around 3,500 cm -1 , corresponding to Hbonded surface OH stretching modes (or strongly held water-related species) [19] was observed for the catalyst calcined at 200°C. The intensity of the band decreased with increasing calcination temperature, and it was very weak and hardly observed when calcination temperature was above 500°C, indicating that strength of water adsorption on the surface of Sn-Nb 2 O 5 /a-Al 2 O 3 catalyst was weakened with increasing calcination temperature.…”