TPD technique

As shown in Fig. 2, the NH3 TPD technique provides information on acid sites over catalysts. While Al-MCM-41-P and Al-MCM-41-D have almost the same acid strengths due to their similar temperature peak of around 250°C, Al-MCM-41-P has more acid sites compared to Al-MCM-41-D. It can be gleaned from this result that the catalytic activity of Al-MCM-P is better than that of Al-MCM-D not because of Al-MCM-P s acid strength but because it has more acid sites. The oil products over... 

The CO-TPD technique together with DFT calculations were previously successfully used to characterize monovalent copper positions in Cu-ZSM-5 and Cu-Na-FER catalysts[4, 5]. Recently it was observed that the CO molecule can also form adsorption complexes, where the CO molecule is bonded between two extra-framework cations [6]. It is likely that the formation of similar species between the Cu+ and K+ ions can also occur. The presence of adsorption complexes on such heterogeneous dual cation site was evidenced by the FTIR experiments [7]. The formation of CO complexes on dual cation sites was not considered in our previous TPD models where three types of Cu+ sites were taken into account. 

These TPD techniques reflect the kinetics (not thermodynamics) of adsorption, and are quite useful for determining trends across series of catalysts, but are often not suitable for the derivation of quantitative information on surface kinetics or energetics, in particular on ill-defined real catalysts. Besides averaging the results from desorption from different sites, TPD detection is also complicated in porous catalysts by simultaneous diffusion and readsorption processes [58],... 

IR spectroscopy, 36 107-108 secondary-ion mass spectrometry, 36 107 TPD technique, 36 106-107 determination of adsorbed amounts, 25 195, 196... 

VEEL or RAIR spectroscopy to provide insight into temperature-dependent surface reactions. The TPD technique also provides information about the overall C/H composition of the hydrocarbon layers at different temperatures. Whereas we have made reference to, and taken into account, experimental results obtained from the use of such nonvibrational techniques in many cases, particularly when considering spectral interpretaions, it has not been feasible for us to systematically cover such papers that do not also include vibrational spectroscopic work. 

In relation to gas detection mechanism of the Pd-SnC>2 sensor, the adsorbed state of oxygen was studied by temperature programmed desorption (TPD) technique. 

In the present work, factors influencing the adsorbed state of oxygen on the Pd-Sn02 sensor have been investigated by the TPD technique. Relations between the TPD results and the conductivity changes of the sensor have also been examined. 

Treatment of magadiite with ammonium chloride solutions results in a practically complete removal of the sodium cations, however, only about 40 % of the exchangeable sodium cations are replaced by ammonium, the rest of the cationic sites is occupied by protons. Thus, fully exchanged ammonium magadiite cannot be obtained in presence of water since it undergoes partial hydrolysis. Under the conditions of the applied TPD technique, NH4-[Si]MAG is deammoniated at relatively low temperatures around 130 "C. 

Data on the formation of carbonaceous materials from diene and acetylene over 373 K and selectivity of n-butane in butadiene hydrogenation (H2/BD=2.2, 1.33 kPa BD, 284 K) are collected in Table 3. The hydrogen content of the deposits was calculated from the amount of the self-hydrogenated products in the gas phase. Reaction of 1,3-butadiene was accompanied with formation of n-butenes whereas in reaction of acetylene 1,3-butadiene was the principal product. Hydrogen content of the deposits was also measured by TPD technique. Desorption of H2 is presented in Figure 3 measured on Cat. C before (1) and after BD poisoning at 489 K for 18 hr (2). 

In this work, a Cu0/Ti02 catalyst (10wt% CuO, specific surface area = 120 m /g) was studied in NH3 oxidation. The catalyst was also characterized by NH3 TPD technique and FT-IR spectroscopy in order to obtain information about the nature of active sites for SCO and the occurrenece of competitve adsorption of water on such sites. A mechanism of ammonia oxidation is proposed. 

The formate, formed by oxidative dehydrogenation of the acid, is quite stable and doesn t decompose until 480 K. This decomposition is a classical first-order case with a decomposition activation energy of 130 kJ mol-1 and a normal value pre-exponential of 1013 s-1. The great ability of the TPD technique is the separation of the individual steps in the reaction in temperature. It is clear that the step proceeding over the highest barrier in this case is the formate decomposition, and that in a catalytic oxidation of formic acid the most abundant surface intermediate is likely to be the formate with its decomposition being rate determining. 

These two examples are meant simply to illustrate the utility of the TPD technique in surface reactivity and catalysis, and other examples follow in... 

Alkali metal promoters are known to control acidity in supported metal catalysts. Our studies on alkali promoted Pt/Al203 catalysts through H2-O2 chemisorption. Temperature Programmed Reduction and ammonia TPD techniques have shown that besides the attenuation of acidity, added alkali affects the binding of Pt species on the support, thereby influencing its reducibility and dispersion. Based on the studies above, several aspects of promoter effects in supported platinum catalysts are discussed. 

The growth and reactivity of surface alloy films of Sm/Ru(001) have been investigated by XPS and TPD techniques. A monolayer of Sm is formed on Ru(OOl) surface at 500 K. Beyond this coverage, surface alloy phase is highly favored due to interdillusion process. The chemisorption of CO on this interface is both molecular and dissociative in nature. A new molecular CO species associated with Sm20x is detected in our studies. 

We have recently reported that cerium-exchanged mordenite (CeNa-MOR) is a higjily active and selective catalyst for NO reduction witli ammonia in oxygen-rich conditions [23]. We have furtlier found tliat it oxidizes SO2 to a negligible extent [24, 25], and tliat it appears to flilfill the aforementioned requirements for an ideal NH3-SCR catalyst. In the present paper, we will report on these aspeets of eerium-exchanged zeolite catalysts. Furthermore, its surface interaction with two reactants, NO and NH3, is examined with the temperature programmed desorption (TPD) technique. 

In the following, several examples of application of the TPD technique to the study of surface reactions will be briefly discussed. 

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