Surface acidity determination

Although a variety of amines, particularly trimethylamine and n-butylamine have widely been used as poisons in catalytic reactions and for surface acidity determinations (20), comparably few spectroscopic data of adsorbed amines are available. As with ammonia, coordinatively adsorbed amines held by co-ordinatively unsaturated cations have preferentially been found on pure oxides (176, 193-196), whereas the protonated species were additionally observed on the surfaces of silica-aluminas and zeolites (196-199). However, protonated species have also been detected on n-butylamine adsorption on alumina (196) and trimethylamine adsorption on anatase (176) due to the high basicity of these aliphatic amines. In addition, there is some evidence for dissociative adsorption of n-butylamine (196) and trimethylamine (221) on silica-alumina. Some amines undergo chemical transformations at higher temperatures (195, 200) and aromatic amines, such as diphenylamine, have been shown to produce cation radicals on silica-alumina (201, 201a). 

The above results led to the synthesis of a ceramic acid, 5-10 wt% W-added Sn02 materials calcined at 1000-1100 °C. The surface acidity determined by the heat... 

The above studies resulted in novel ceramic acids, l-5wt%W-added aluminas calcined at 1000-1200 °C. The surface acidity determined by the heat of adsorption of Ar and the catalytic activity for decompositions of toluene, ethylbenzene, and cumene were higher than those of sihca-alumina. The crystallographic phase was 0- or a-Al203. 

The data on the catalytic activity of the synthesized samples of CoO/H -pentasils in the NO+O2 NO2 reaction and acidic properties of these san les characterized by total surface acidity determined by TPDA method are given in Table 2. It is seen that 10% CoO... 

This communication is part of a research program aimed at a systematic investigation of the preparation procedure of MoP/AljO, mild-hydrocracking catalysts. Essentially, we study the effect of phosphorus incorporation sequence on the state of dispersion of the active phase, surface acidity and physical properties. For this purpose, the samples were characterized using the following physico-chemical techniques BET surface area, mechanical strength, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), surface acidity determined by pyridine adsorption. 

Perhaps the simplest case of reaction of a solid surface is that where the reaction product is continuously removed, as in the dissolving of a soluble salt in water or that of a metal or metal oxide in an acidic solution. This situation is discussed in Section XVII-2 in connection with surface area determination. 

IR spectroscopy of two supports was used for the determination of their surface acidity. The presence of Lewis acid sites on the surface of sepiolite allowed the preparation of a catalyst able to transform citral into menthol in fairly good yield under veiy mild conditions (90°C, 1 barH2). 

Xiang, T.-X. Anderson, B. D., Phospholipid surface density determines the partitioning and permeability of acetic acid in DMPC cholesterol bilayers, J. Membrane Biol. 148, 157-167 (1995). 

Chemical composition was determined by elemental analysis, by means of a Varian Liberty 200 ICP spectrometer. X-ray powder diffraction (XRD) patterns were collected on a Philips PW 1820 powder diffractometer, using the Ni-filtered C Ka radiation (A, = 1.5406 A). BET surface area and pore size distribution were determined from N2 adsorption isotherms at 77 K (Thermofinnigan Sorptomatic 1990 apparatus, sample out gassing at 573 K for 24 h). Surface acidity was analysed by microcalorimetry at 353 K, using NH3 as probe molecule. Calorimetric runs were performed in a Tian-Calvet heat flow calorimeter (Setaram). Main physico-chemical properties and the total acidity of the catalysts are reported in Table 1. 

Example 2.1 Evaluation of Surface Charge from Alkalimetric and Acidimetric Titration Curves and Determination of Surface Acidity Constants... 

Figure 6. Use of Method I, Equation 22, to calculate surface acidity constants with Ng - 12 sites nm" log Ka = -3.5 and log Ka2 = -8.1 or, in other terms, pHZpC = 5.8 and log Kd - -2.3. Capacitances were determined from the slopes according to Equation 22 acid branch, 0.77 F m base branch, 0.89 F m. Data are from Figure 5, Ti02 in 0.1 M KNO3 (32). ...

Metal oxides, 31 78-79, 89, 102, 123, 157-158, 191, 32 199-121 see also Amorphous metal oxides Sulfate-supported metal oxides specific oxides adsorbed oxygen on, 27 196-198 binary, surface acidity, 27 136-138 catalytic etching, 41 390-396 coordination number, 27 136 electrocatalysts, 40 127-128 Fe3(CO)i2 reaction with, 38 311-314 Lewis acid-treated, 37 169-170 multiply-valent metals, electrocatalytic oxidations, 40 154-157 superacids by, 37 201-204 surface acidity, methods for determining, 27 121... 

Surface photovoltage spectroscopy (SPS) in Fig. 6.5 was used to determine the surface acidity of JML-1 by measuring transition of electrons between the interface and the surface. The JML-I40 calcined at 550°C exhibited two peaks at 596 nm and 677 nm, whereas the sample without calcination had only one peak at 330 nm. The peak at 330 nm is assigned to the band-band electron transition and those at 596 nm and 677 nm are attributed to the surface-related transitions. The observation of these surface-related transitions indicates the presence of positive charges on the surface of the calcined sample, suggesting that the acidity of JML-1 catalyst is resulted from a large amount of SZ acidic sites on the silica surface. 

In the mechanism illustrated in Figure 6, the combination of the redox and acid properties of the catalyst determines the relative contribution for the formation of MA and PA. It is generally accepted that the higher the crystallinity of the VPP, the more selective to PA is the catalyst (3,4,10-12,17,18). Poorly crystalline VPP, like that one formed after the thermal treatment of the precursor (especially when it is carried out under oxidizing conditions), is selective to MA, but non-selective to PA. On the contrary, a fully equilibrated catalyst, characterized by the presence of a well-crystallized VPP, yields PA with a good selectivity. The presence of dopants that alter the crystallinity of VPP may finally affect the MA/PA selectivity ratio (19). Moreover, the surface acidity also influences the distribution of products (17) an increase of Lewis acidity improves the selectivity to PA, while that to MA is positively affected by Bronsted acidity (2). 

Carboxylic acids The smallest carboxylic acid, formic acid, can be measured using infrared spectroscopy (Table 11.2), since it has characteristic absorption bands. As discussed earlier and seen in Fig. 11.33b, mass spectrometry with chemical ionization using SiF5 also revealed HCOOH in an indoor environment (Huey et al., 1998). However, since the sensitivity in these initial studies was about two orders of magnitude less than that for HN03, the detection limit may be about the same as that for FTIR and TDLS. Formic and acetic acids have been monitored continuously from aircraft (Chapman et al., 1995) and their surface flux determined by eddy correlation (Shaw et al., 1998) using atmospheric pressure ionization mass spectrometry. Detection limits are about 30 ppt. 

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