Probe molecules isopropanol

A similar technique has been used to determine the acidic character of niobium oxide and niobyl phosphate catalysts in different solvents (decane, cyclohexane, toluene, methanol and isopropanol) using aniline and 2-phenyl-ethylamine as probe molecules [27, 28]. The heat evolved from the adsorption reaction derives from two different contributions the exothermic enthalpy of adsorption and the endothermic enthalpy of displacement of the solvent, while the enthalpy effects describing dilution and mixing phenomena can be neglected owing to the differential design and pre-heating of the probe solution. 

Examination of the reaction pathways of probe molecules has also been applied to the characterization of basicity. In this method, a suitable probe molecule is selected with the intention that base sites will convert it uniquely to a given product. The conversion of isopropanol has been widely applied in this context. 

Isopropanol was used as a probe molecule to characterize the acidity of heteropolyacid compounds because the product s distribution upon reaction depends on the nature of the surface active sites. Strong Brdnsted (H ) and Lewis acid sites catalyze the dehydration of isopropanol to propylene (di-isopropyl ether over weak Lewis acid sites), and redox/basic sites lead to the dehydrogenation of the alcohol to acetone. 

The presence of acidic sites on the POM pillars enables the LDH-POM to act as acid/base bifimctional catalysts or even as strongly acidic catalysts (251-253,468). As mentioned previously, isopropanol is a probe molecule for distinguishing between acidic and basic catalysis. For example, ZnAl-SiWiiM04o-LDH (M = Mn, Fe, Co, Ni, Cu, and Zn divalent ions) has been used as the catalyst for the decomposition of isopropanol to give propene almost exclusively (98%, reaction (B)) at 90% conversion (251). 

Isopropanol as a Probe Molecule Redox versus Acid Properties of... 

Banares, M.A. and Wachs, I.E. Molecular structures of suported metal oxide catalysts under different environments. J. Raman Spectrosc. 2002, 33, 359-380. Gambaro, LA. and Briand, L.E. In-situ quantification of the active acid sites of H6P2Wis062J H20 heteropoly-acid through chemisorption and temperature programmed surface reaction of isopropanol. Appl Catal 2004, 264, 151-159. Badlani, M. Methanol A Smart Chemical Probe Molecule. Master thesis, Lehigh University, Bethlehem, PA, 2000. 

Qualitatively similar results were obtained for reaction and desorption of normal and iso-propanol on the 011 [-faceted TiO2(001) surface. In the case of normal propanol, almost half of the molecules initially adsorbed desorbed as the parent molecule at 370 K, while half of the remaining surface species reacted to form propanol at 580 K. The ratio of propene to propionaldehyde generated at 580 K was 10 1. Desorption of isopropanol quantitatively mirrored the desorption of normal propanol in two desorption states at 365 and 512 K. Isopropanol did not generate any dehydrogenation products (e.g., acetone), and the surface did not generate any bimolecular coupling products for any of the probe alcohol molecules. The absence of ether formation on the (Oil [-faceted surface is consistent with the need for double-coordination vacancies to facilitate that reaction, and the absence of such sites on this surface of titanium dioxide [80]. 

The previous sections discussed the applications of methanol chemisorption as a tool to describe the surfaces of oxide catalysts. Other molecules, such as isopropanol and formic acid, have also been used as chemical probes to measure the number of surface active sites of metal oxide catalysts but to a lesser extent. The ability of isopropanol to distinguish between surface redox and acid sites and the observation that it adsorbs as a stable monolayer of surface isopropoxy species over oxide materials, also makes this molecule a suitable surface chemical probe. 

The charecterization of microporosity in two sets of activated charcoal is carried out here along two main lines. The first is the extension of Sing s ctj method to the case of adsorption of various molecules (iodine, salicylic acid, ter-butanol and 3-methyl-3-pentanol). Only primary filling of the raicropores is then detected. The second approach uses two sets of flat (benzene, naphthalene, pyrene and perylene) or more bulky (methanol, isopropanol, ter-butanol and 3-methyl-3-pentanol) molecular probes which evidence the existence of slit-shaped and bottle-necked micropores. 

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