A technique for the quantitative determination of adsorbed species on zeolites and other solids was designed by coupling infrared spectroscopy and in situ thermogravimetry. The weight of H-Y zeolites in an infrared spectrometer was monitored upon pyridine adsorption by a McBain type microbalance. Improved extinction coefficients for the pyridinium band and for ν(OH) bands were determined on these reference materials. The influence of the temperature used for desorption of physisorbed pyridine was studied.

Several zeolites (cubic and hexagonal faujasites, steamed or not) are tested as acid catalysts. The strength and number of Brönsted acid sites are determined from FTIR studies of adsorbed probe molecules (CO, pyridine). Direct benzene hydrogenation leading to cyclohexane is observed only at low temperature (500K) with the less acid zeolites (H0=−8.5). Side-reactions grow progressively with the acid strength of the catalyst and, in some cases, with increasing reaction temperature (in other cases, a drastic deactivation is observed). Coke is generated by the more acid hydroxyl groups (H0=−12). The occurrence of the various steps of the scheme describing the benzene hydroconversion process depends on the strength of Brönsted acid sites and reaction temperature.

We describe a series of steamed HNaY zeolites containing large amounts of unusual (3700)OH groups. The method of steaming and the solids obtained are well described. These hydroxyl groups are thermally stable and characterized by their weak acid strength measured by CO adsorption at low temperature: Δν(OH)≈145 cm−1 i.e. H0=−5, slightly dependent on the coverage level. Their number is estimated at 11.8 per unit cell. Interesting catalytic properties are expected for these (3700)OH groups since the unusual soft acidity would prevent cracking and coke formation in some acid-catalyzed reactions. Moreover, the (3670)OH groups are obtained in significant amount after soft leaching of the steamed zeolite with NH4+ solutions. This solid is highly crystalline (≈85%), therefore, after CO adsorption, the shift of the (3670)OH groups is unambiguous: Δν(OH)=185cm−1 i.e. H0=−6.

This chapter discusses the comparative properties of modified HEMT and HY zeolites from the Fourier transform infrared spectroscopy (FTIR) study of carbon monoxide (CO) adsorption. Progressive CO adsorption has been studied by FTIR spectroscopy on two series of acid-leached steamed HEMT and HY zeolites with various silicon (Si)/AlF ratios. Acidity of structural hydroxyl (OH) groups of steamed hexagonal faujasites is determined and compared with the results obtained with the cubic series.Quantitative estimation of the Brönsted acidity of extraframework phase (numbers and strength) is carried out and allowed to complete the comparison between the two structural varieties. Only minor differences are detectable.

This chapter discusses the preparation, characterization, and catalytic testing of sulfur resistance of Platinum palladium (PtPd) catalysts. Platinum (Pt), palladium (Pd), and PtPd metallic precursors are deposited on amorphous silica aluminas and dealuminate FAU zeolites. The catalytic activity is measured in the hydrogenation of toluene in the absence or presence of sulfur. In the absence of sulfur, alloying Pt with Pd decreases the hydrogenation activity. Catalysts made from ammoniated precursors are most active with one remarkable exception. In the presence of sulfur, thioresistance is a function of reaction temperature––that is, the sulfur coverage of the metallic phase. Pd increases sulfur resistance. The effect of support acidity on thioresistance is observed only at high sulfur coverage.

Some properties of hexagonal and cubic, highly crystalline faujasites are compared by means of two sorbed probes (pyridine and CO) studied by FTIR spectroscopy. Whatever the structural variety, the acid strength of the HF and LF hydroxy groups and the (LF)OH contribution to the pyH(+) species increase with the Si/Al-F ratio. A nu(CO/LF) band detectable between 2160 and 2167 cm(-1) is assigned to the formation of the (LF)OH ... CO complex, its wavenumber value depends on the dealumination and coverage levels. The molar absorption coefficients, epsilon, of the HF and LF bands of HEMT zeolite are similar to those of HF and LF bands of HY zeolite, respectively. No structural effect is detectable. The progressive CO adsorption confirms the epsilon(HF) value previously determined by pyridine adsorption, and the results obtained for epsilon(LF) are discussed.

Progressive CO adsorption has been studied by IR spectroscopy, at low temperature on acid-leached steamed Y zeolites and on two silica-alumina samples with different Si/Al ratios. The IR spectra of the steamed Y zeolites are complex in the v(OH) range. After CO adsorption only some perturbed v(OH) and v(CO) bands had previously been assigned. This study showed that some specific Bronsted acid sites observed in steamed Y zeolites were also present in silica-alumina samples, allowing us to relate them to silica-alumina debris. On the silica-alumina samples, the more acidic site strength [characterized by a perturbed v(OH) band near 3450 cm(-1)] was found to be close to that of the high-frequency (HF)OH groups of non-dealuminated HY zeolites. A quantitative estimation of such sites was obtained by determination of the molar absorption coefficient epsilon(CO) of the corresponding perturbed v(CO) band.

Lors de l'adsorption progressive de CO sur les hydroxyles MF de zéolithes HY et HEMT, la bande ν(OH associé) glisse vers les hauts nombres d'onde lorsque le taux de recouvrement augmente. L'interprétation de cette observation déjà mentionnée dans la littérature suscite quelques controverses. Nos résultats montrent que l'évolution de la bande n'est pas due à l'hétérogénéité intrinsèque de l'acidité des (HF)OH. La co-adsorption de deux sondes (pyridine, CO), l'étude de leur adsorption sur des zéolithes désaluminées et la modélisation de la distribution des (HF)OH dans les supercages permettent de conclure à des effets dus à la sonde.

As increasing amounts of CO are adsorbed on the HF hydroxyls of HY and HEMT zeolites, the Delta nu(OH) shift observed decreases progressively. This experimental result already mentioned in the literature has given rise to a controversy because of its various interpretations. Our studies show that the progressive shift is not due to an intrinsic acid strength heterogeneity. The simultaneous adsorption of two probes (pyridine, CO), the results observed on dealuminated zeolites and the (HF)OH distribution in the large cavities demonstrate effects due to the sorbed molecules.

Two zeolites were coked using cyclohexene at 620 K; one had a low Si/Alf ratio (HY), the other was ultrastabilized (HYS). It was found that oxygen regeneration occurred at 770 K or above, whereas ozone was effective at 450 K or less,e.g. under conditions such that the HY sample was still thermally stable.

HEMT zeolites steamed over a wide temperature range (720 - 1010 K) unleached or leached with HCl(1N) were characterized by spectroscopic techniques and chemical analyses. Strong Bronsted acidity was quantified by pyridine adsorption at 470 K. Dealumination and acidity results of two series of cubic and hexagonal steamed faujasites are matched.

Two series of steamed HY zeolites progressively leached with HCl(IN), were studied by FTIR. The numbers of each zeolitic hydroxyl type were determined by analysis of the complex v(OH) massif. The numbers of zeolitic hydroxyls remain nearly constant for a wide range of acid leaching, during progressive extraction of Al extraframework species, however, the relative quantities of strongly acidic hydroxyls go through a maximum for a mild leaching. The catalytic activity of these zeolites for benzene hydroconversion confirms their acidities.

A laboratory scale rotating reactor designed for high temperature treatments of powders under controlled atmosphere is described. It was used for HY zeolite steamings. This rotating reactor allowed the lattice dealumination level to be governed with a good accuracy and to minimize concomitant amorphization. A series of well-defined steamed HY zeolites characterized by their lattice Si/Al ratio varying from 7.6 to 40 was obtained.

Benzene hydroconversion, catalyzed by steamed HY zeolites, leads to direct hydrogenation, cracking and alkylation reactions. The respective conversion maxima observed versus the time on stream on the catalyst are explained as the result of two simultaneous effects: accumulation of the active species onto the solid, and deactivation of the cracking and alkylation sites.

A series of HY zeolites partially amorphized by heating, steaming and/or irradiations with Ar(17(+)) and Xe(43(+)) ions was studied by IR spectroscopy in the 1100-500 cm(-1) range. Results show that the simple relations between N(Al-fram) and the wavenumber of structural bands nu(1) and nu(2) (c.a. 1050 and 800 cm(-1) respectively) can be applied only with zeolites containing a small amount of amorphous phases. In contrast, a weak, well-defined band, nu(3) (c.a. 600 cm(-1)) allows one to determine bath the N(Al-fram) and crystallinity level from its wavenumber and intensity, respectively.

Selective adsorption of pyridine was studied by infrared (IR) spectroscopy at 470 K on a series of HY zeolites, including samples dealuminated either by isomorphous substitution or steaming followed by acid leaching. Molar extinction coefficients of framework hydroxyls at high and low frequency, ϵHF and ϵLF, and of pyridinium ions characterized by the 1545 cm−1 band, ϵpyH+, were determined. These values do not vary with the Si/AlF ratios. In the case of steamed samples, strongly acidic sites give rise to additional OH bands at 3596 and 3522 cm−1. Pyridine adsorption at 620 K allows their mean molar extinction coefficient, \̄ge3596 + 3522, to be determined. From the decomposition/deconvolution of the v(OH) massif of acidic OH groups, it is possible to count each type of acidic OH group and, by comparison with the number of framework Al per unit cell, to determine the cationic charges of extraframework Al-containing species counterbalancing the negative framework charge. This study evidences the substantial contribution of the (3522)OH groups; moreover, the results are in agreement with the assumption that 3596 and (3522)OH bands are due to the shift of the HF and LF framework hydroxyls, respectively, provoked by the presence of extraframework species.

HY zeolites,s´teamed at medium temperature (800 K), catalyze the reactions of benzene self-alkylation and hydrogenation under the pressure of hydrogen. Products of cracking and coke accompany the formation of toluene, methylcyclopentane, and cyclohexane. At 650 K, the maximum conversions in alkylation and hydrogenation exceed 30% and 7% respectively, and remain high for a few days (WHSV = 0.25 h−1). The i.r. study (C2H4, pyridine) shows that active zeolites contain strongly acidic Bro¨nsted sites, characterized by a νOH band at 3600 cm−1, and Lewis sites. A linear correlation exists between the catalytic activity and the number of highly acidic OH groups. This unexpected reaction at 600–650 K may form an interesting catalytic test of very acidic materials.

Acid-leached and unleached Y zeolites dealuminated by steam calcination have been characterized by spectroscopic techniques and chemical analysis. Measurement of the free volumes of the supercages has been carried out by benzene adsorption. The experimental results are mathematically conclusive, and it appears that the amorphous phase obtained after dealumination is quasi-aluminous (SiO2 < 5%) of which 65% is localized in the supercages. The zeolitic framework is conserved during partial dissolution of the extralattice aluminous fraction, but 10% of it is destroyed during strong acid leaching and the silica is then exposed. The same technique can be used to localize a solid additive obtained after impregnation of the Y zeolites.

Y zeolites exchanged with palladium or chromium ions react at 570 K with H-2S or a mixture of H-2 + H-2S. Under the action of H-2S, nearly all the Pd(II) ions are converted into PdS, with water eliminated, whilst with the H2 + H2S mixture, reduction to Pd(0) competes with sulphurization. Cr(VI) is drastically reduced by H-2S, starting at 470 K. Easily desorbable elemental sulphur is formed, but no chromium sulphide is obtained. Cr(III) and Cr(II) ions are slowly reduced by H-2S. In the bimetallic zeolite PdCrY, sulphurization of the Pd(II) is not sensitive to the presence of the chromium ions.

The sorption of benzene over a series of CrNaHY zeolites has been measured at 370–530 K. Although neither series of isotherms entirely satisfies the Langmuir or Dubinin model, both formulae give identical values for the saturation limit. The free volumes were found to decrease with increasing H + or Cr n+ ion concentration, and have been related to extra-framework phases. The initial heats of sorption indicate that the affinity of benzene for the different sorption sites varies in the order Na + > Cr n+ ≃ H + . For the sodium-rich zeolites, it was found that the sorption heats increase at temperatures above 430 K.