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The acid sites on γ-Al2O3 were characterized using FTIR spectroscopy of adsorbed pyridine and temperature programmed desorption (TPD) of 2-propanamine, ethanol, 1-propanol, 2-propanol, and 2-methyl-2-propanol, together with density functional theory (DFT) calculations. Following room-temperature adsorption and evacuation, the surface coverages of the adsorbed alcohols were between 2 and 3.2 × 1018 molecules/m2. For each of the adsorbed alcohols, reaction to olefin and water products occurred in a narrow peak that indicated reaction is a first-order process with a well-defined activation energy, which in turn depended strongly on the particular alcohol. DFT calculations on an Al8O12 cluster are in excellent agreement with the experimental observations and show that the transition states for dehydration had carbenium-ion character. The carbenium ion stability in terms of proton affinity (of alkenes) matches well with the activation energy of the dehydration reaction. Adsorption of water on the γ-Al2O3, followed by evacuation at 373 K, demonstrated that water simply blocks sites for the alcohols without affecting the reaction activation energy. There was no evidence for Brønsted sites on the γ-Al2O3 based on FTIR of pyridine or TPD of 2-propanamine.

The adsorption properties of framework Sn sites in a siliceous zeolite beta were examined by comparing the adsorption of acetonitrile, diethyl ether, and 2-methyl-2-propanol on a Sn-Beta zeolite, a purely siliceous Beta zeolite, and a siliceous Beta zeolite with impregnated SnO2, using temperature-programmed desorption (TPD) and thermogravimetric analysis (TGA). Adsorption stoichiometries close to one molecule per framework Sn site were observed for each of the probe molecules. Although the 1:1 complexes with acetonitrile and diethyl ether decompose reversibly upon mild heating in vacuo, the 1:1 complex formed by 2-methyl-2-propanol underwent dehydration to butene and water over a very narrow temperature range centered at 410 K. FTIR spectra of acetonitrile-d3 at a coverage of one molecule per site exhibit a υ(C–N) stretching frequency at 2312 cm–1 that is not observed with nonframework Sn, providing a convenient method for characterizing the presence of framework Sn sites. Water interacts strongly enough with the Sn sites to prevent adsorption of acetonitrile.

The catalysts, Ti 0.9 M 0.1 O 2-δ (M ) Cr, Mn, Fe, Co, Cu), were synthesized in anatase phase by solution combustion. Selective catalytic reduction (SCR) of NO with NH 3 was investigated over these catalysts. The reaction occurred at the lowest temperature over Ti 0.9 Mn 0.1 O 2-δ , but the selectivity for N 2 was highest over Ti 0.9 Fe 0.1 O 2-δ . Therefore, both Mn and Fe were substituted in TiO 2 (Ti 0.9 Mn 0.05 Fe 0.05 O 2-δ ). The reaction occurred at low temperature with a high selectivity over this catalyst. In order to understand the reaction mechanism and the nature of the active sites, temperature programmed desorption (TPD) of NH 3 and hydrogen uptake studies were carried out. The relation between the Lewis acid sites and SCR window and the relation between Bronsted acid sites and low temperature was established. The order of the SCR reaction with respect to NO, NH 3 , and O 2 was also investigated. It was also shown that the N 2 selectivity of the SCR reaction has a strong inverse correlation with the oxidation of ammonia.