Pyridine temperature-programmed desorption

J.M. Campelo, A. Garda, D. Luna, J.M. Marinas, A. A. Romero, Characterization of acidity in AIPO4-AI2O3 (5-15 wt% AI2O3) catalysts using pyridine temperature-programmed desorption. Thermochim. Acta. 265,103-110 (1995). doi 10.1016/0040-6031(95)02379-G... 

Figure 4 Temperature programmed desorption of pyridine pyridine adsorbed at 47SK, heating rate 20K/mtn...

This clearly indicates that the support is able to convert a fraction of methane but contributes primarily to coking To investigate the role of acid sites in the conversion of methane to coke and hydrogen, the acid sites of the catalysts were characterized by sorption and temperature programmed desorption (t.p.d) of pyridine T.p.d. of pyridine (see Fig. 4) suggest a higher... 

As stated above, when probes with specific adsorption characteristics are used, additional chemical information can be extracted from adsorption-desorption experiments. Temperature-programmed desorption (TPD) in particular is often employed to obtain information about specific sites in catalysts [55,56], The temperature at which desorption occurs indicates the strength of adsorption, whereas either the amount of gas consumed in the uptake or the amount of desorption upon heating attests to the concentration of the surface sites. The most common molecules used in TPD are NH3 and C02, which probe acidic and basic sites, respectively, but experiments with pyridine, Oz, H2, CO, H20, and other molecules are often performed as well [57-59], As an example, the ammonia... 

Tomida et al. (73) investigated the temperature-programmed desorption of n-butylamine from silica-alumina and alumina. The desorbed amine products were different in the two cases. n-Butylamine and n-butene were obtained from silica-alumina dibutylamine and n-butene were obtained from alumina. In a subsequent paper by Takahashi et al. (73a), the authors conclude that two types of adsorption sites on silica-alumina account for the desorption behavior of n-butylamine. One type chemisorbs the amine and the other catalyzes the decomposition of the amine to lower olefins at temperatures above 300°C. On the other hand, amine decomposition was not observed when pyridine was desorbed from silica-alumina. The effects of sodium poisoning on desorption behavior of n-butylamine and pyridine were also examined. 

In the last decade, a number of publications has been devoted to this subject. These studies are either based on spectroscopic techniques (IR, NMR) or on desorption techniques (temperature programmed desorption of pyridine and water). In all of these models the distinction between free and bridged silanols, trapped water and intraglobular hydroxyls is the key problem. 

Dealuminated M-Y zeolites (Si/Al = 4.22 M NH4, Li, Na, K, Cs) were prepared using the dealumination method developed by Skeels and Breck and the conventional ion exchange technique. These materials were characterised by infrared spectroscopy (IR) with and without pyridine adsorption, temperature-programmed desorption (t.p.d.) of ammonia. X-ray difiracto-metry (XRD) and differential thermoanalysis (DTA). They were used for encapsulation of Mo(CO)5. Subsequent decarbonylation and ammonia decomposition was monitored by mass spectrometry (MS) as a function of temperature. The oxidation numbers of entrapped molybdenum as well as the ability for ammonia decomposition were correlated to the overall acidity of the materials. It was found that the oxidation number decreased with the overall acidity (density and/or strength of Bronsted and Lewis acidity). Reduced acidity facilitated ammonia decomposition. 

PC spectrophotometer equipped with a reflectance attachment. FTIR of pyridine adsorbed and temperature-programmed desorption (TPD) of ammonia methods has been previousiy reported [10]. 

Chemical methods of determining the nature and surface concentrations of active components have also been attempted Mo oxide by butene adsorption and, in reduced catalysts, by oxygen chemisorptionM0S2 and/or active site concentrations by pyridine adsorption and thiophen adsorption and temperature-programmed desorption of thiopen cf. p. 200), surface acidity by NH3 adsorption cf. p. 199). Sulphides in a Ni-Mo/ AI2O3 catalyst have been characterized by differential thermal analysis of the catalyst in oxygen. ... 

The hydrothermal deactivation of Y zeolite containing 0, 4, 7 and 12 wt.% of REO and its effects on catalytic activity, stability and selectivity were investigated. The Y zeolites were hydrothermally deactivated at 788°C in three consecutive cycles of two hours each. The fresh and deactivated zeolites were characterized by measuring Unit Cell Size (UCS) and surface area. The acidic properties were measured by the Temperature Programmed Desorption (TPD) of ammonia and IR-pyridine desorption. In order to correlate structural, textural and acid properties with catalytic behavior, the zeolites were evaluated in the conversion of cyclohexane. The Hydrogen Transfer Index (HTI) measured as a ratio of paraffins to olefins is a parameter of the selectivity. It was found that the REO was incorporated into zeolite structure up to high concentrations modifying to some extent XRD deflection, the acidic properties and the HTI ratio. After deactivation, the acidity and HTI were diminished and the Lewis/Bronsted acid ratio was modified. HTI decreased as REO concentration increased. 

The powder X-ray diffraction patterns were measured in a D-500 SIEMENS diffractometer with a graphite seeondary beam monochromator and CuKoj contribution was eliminated by the DIFFRAC/AT software to obtain a monochromatic CuKa,. The Unit Cell Size (UCS) was measured following the ASTM D-3942-90 procedure. The Surface areas were measured by nitrogen adsorption at 75 K on a Micromeritics Accusorb 2100 E equipment using the ASTM method D-3663-78. Temperature Programmed Desorption (TPD) of ammonia and pyridine adsorption by Infrared Spectroscopy (IR) were used to characterize the acidity of the zeolites. For IR-Pyridine the spectra were recorded each 100°C and the characteristic bands of Lewis and Bronsted acid sites (1444 cm" and 1540 cm, respectively) were integrated in order to obtain the total acid sites. 

Schwarz, Russell, and Harnsberger have developed a technique combining transmission infrared spectroscopy and temperature-programmed desorption and used it to study the interaction of pyridine with three silica-aluminas. On the 10 wt % AI2O3, acid sites were calculated to be 0.27 [xmole m (84% Lewis acid sites under experimental conditions). The activation energies for... 

The catalysts were characterized by using various techniques. X-ray diffraction (XRD) patterns were recorded on a Siemens D 500 diffractometer using CuKa radiation. The specific surface areas of the solids were determined by using the BET method on a Micromeritics ASAP 2000 analyser. Acid and basic sites were quantified from the retention isotherms for two different titrants (cyclohexylamine and phenol, of p/Ta 10.6 and 9.9, and L ,ax 226 and 271.6 nm, respectively) dissolved in cyclohexane. By using the Langmuir equation, the amount of titrant adsorbed in monolayer form, Xm, was obtained as a measure of the concentration of acid and basic sites [11]. Also, acid properties were assessed by temperature-programmed desorption of two probe molecules, that is, pyridine (pKa= 5.25) and cyclohexylamine. The composition of the catalysts was determined by energy dispersive X-ray analysis (EDAX) on a Jeol JSM-5400 instrument equipped with a Link ISI analyser and a Pentafet detector (Oxford). 

Population of surface acid sites determined by temperature-programmed desorption of pyridine and cyclohexylamine ... 

Temperature programmed desorption [10-14] of pyridine and ammonia was carried out in a self made apparatus with 0.5 g of catalyst. The desorption profiles were recorded in the range of 100 to 450 °C (600 °C with NH3) at 10 °C intervals using 50 ml/min argon (pyridine) or helium (NH3) as carrier gas. Detection of the desorbed compounds took place with a quadrupole mass spectrometer (Hiden DSMS). 

Adsorption and wetting Adsorption of gases and vapors, combined with IR spectroscopy, microcalorimetry, and so forth Temperature-programmed desorption of absorbed substances (ammonia, pyridine, and so forth, coupled with mass spectrometry and IR spectroscopy Heats of adsorption, specific surface area, pore size distribution, average pore diameter, and fractal dimension Acidic functional groups, relative acid strength ... 

Temperature programmed desorption (t.p.d.) of pyridine The variations of the rates of desorption of pyridine from SAP05-1 and SAP05-3 during... 

The temperature-programmed desorption (TPD) of pyridine was used for characterizing the Y-type zeolites. A wafer of 10 mg of zeolite was activated under vacuum ( 10 Pa) at 673K for 2h. After cooling to 473K, the sample was exposed to pyridine and Ih-outgased. Pyridine desorption was minitored with a 8alzers QMG 311 mass spectrometer. 

Chap. 1 of the present series (see also Fig. 11). Similarly, the amounts of Bronsted and Lewis centers are often measured via pyridine adsorption, and the strength of such acid sites in zeolites is frequently determined by temperature-programmed desorption of previously adsorbed pyridine (see, e.g., [38]). 

Selli and Forni [702] performed a detailed comparison of the determination of surface acidity by FTIR of pre-adsorbed pyridine on the one hand and temperature-programmed desorption of pyridine on the other, where the adsorbents were of Y-, Beta- or MOR-type. An important result of this study appears to be that the pyridine distribution between Br0nsted and Lewis acid sites imder equilibrium conditions (in FTIR) is not much different from that determined under kinetic control (in TPD). 

Temperature-programmed desorption of absorbed substances (ammonia, pyridine, and so forth, coupled with mass spectrometry and IR spectroscopy... 

Studies of pyridine interaction with siliceous surfaces are numerous and have been completed using a variety of techniques including temperature programmed desorption [28], DRIFTS [29] and many others. The original contribution made by this author in the first edition of... 

I. Gillis-D Hamers, I. Comelissens, K.C. Vrancken, P. Van Der Voort, and E.F. Vansant, Modeling of the Hydroxyl Group Population Using an Energetic Analysis of the Temperature-Programmed Desorption of Pyridine... 

Figure 8.7 Temperature programmed desorption/IR of pyridine adsorbed on (above left) H-ZSM-5, (above right) calcined MgAPO-36 and (below) calcined MgAPO DAF-1. All absorbances are from chemisorbed pyridine resolved bands from pyridine adsorbed on Bronsted sites (B) and Lewis sites (L) are annotated.

This concerns mainly acidic and basic properties and has been described by many authors for instance in ref. 67 for acidity and 68 for basicity and 69 in general and also in this book by D. Barthomeuf. The use of infra red spectroscopy and temperature programmed desorption of basic (NH, pyridine, piperidine, n-butylamine...) or acidic (pyrole, CO2,... 

TABLE 1. Temperature Programmed Desorption of Pyridine from Broensted sites in Faujasitic zeolites. (Pyridine = 0.27 mmolg" ), Pyridine sorbed after deammoniation [13]... 

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