József Valyon

On the interpretation of the NH3-TPD patterns of H-ZSM-5 and H-mordenite

Abstract The species obtained from adsorption of ammonia over zeolite H-ZSM-5 and H-mordenite were characterized by temperature-programmed desorption (NH 3 -TPD) and infrared spectroscopy (IR). At ammonia loadings of NH 3 /Al>1, the IR spectra indicated the formation of NH 4 + · n NH 3 associations, where n ⩾1. At loadings of NH 3 /Al 4 + ions and Lewis-bound NH 3 were recorded. The decomposition of the NH 4 + ions and desorption of NH 3 from strong Lewis acid sites gave rise to TPD peaks above about 673 K. The peaks at temperatures lower than about 673 K were assigned to ammonia released from protonated NH 3 associations.

Alkylation of toluene with methanol on commercial X zeolite in different alkali cation forms

Abstract Catalytic alkylation of toluene with methanol was studied at atmospheric pressure, 698 K, and toluene/methanol = 5 mol/mol in a fixed bed reactor. Catalysts were prepared from the Na form of a commercial, pelleted X-type zeolite by ion exchange with alkali cations. Selectivity for side-chain alkylation increased when alkali hydroxide solution instead of alkali salts was used for ion exchange. High selectivity for ethylbenzene formation was achieved on zeolites in the K or Cs form containing excess alkali hydroxides. The turnover number in side-chain alkylation increases with the decreasing amount of strongly adsorbed pyridine or acetic acid per cation.

A study of the acidic and catalytic properties of pure and sulfated zirconia–titania and zirconia–silica mixed oxides

Protonated pyridine (PyH+) was not found on ZrO2 (Z) or ZrO2–TiO2 (ZT), but was detected on sulfated oxides (Z‐S, ZT‐S) by IR spectroscopy. In contrast, ZrO2–SiO2 samples containing about 30–80 mol% ZrO2 showed Brønsted acidity both in non‐sulfated (ZS) and sulfated (ZS‐S) forms. The total acidity was determined by NH3‐TPD. Introduction of sulfate ions increased the site‐specific catalytic activity (TOF) in the conversion of cyclopropane or n‐hexane. The effect of sulfate ions was more significant on samples rich in zirconia. Results suggest that Zr is homogeneously distributed in ZS samples rich in silica. Zirconia‐bound dimeric sulfate, generating strong acidity, could not be formed in these preparations due to the absence of fairly large ZrO2 domains.

An NH3-TPD and -FR study on the acidity of sulfated zirconia

Abstract Temperature-programmed desorption (TPD) and frequency response (FR) methods were used to study the dynamics of ammonia sorption over sulfated zirconia (SZ). The results were interpreted in comparison with results obtained for zirconia (Z) sulfated zirconia–titania (SZT) and zeolite H-ZSM-5 (HZ). Strong Lewis (L) and Bronsted acid (B) sites were detected on each of the samples. NH3 was found to bind to species formed from ammonia on the L and B sites (sites Ll and Lb) by H-bonds. The H-bound ammonia was released at lower temperatures than that directly bound to the B and L sites. FR resonance signals were ascribed to sorption processes over sites B, Lb, and Ll. The L sites were fully covered by NH3 up to the highest temperature of the FR measurement, therefore, these sites could not be detected. For SZ and SZT, the FR intensity was found independent of the temperature suggesting that these samples contain energetically heterogeneous sorption sites.

Mixed-metal pillared layer clays and their pillaring precursors

Mixed-metal pillared layer clays (Fe,Al-PILCs and Cr,Al-PILCs) of various compositions and the pillaring precursors have been prepared and characterised with a combination of chemical and instrumental methods. Chemical analysis data, IR, 57 Mossbauer and 27 Al NMR spectroscopic measurements on the precipitated pillaring precursors and comparison of redox behaviour [temperature-programmed reduction (TPR) results and 57 Fe Mossbauer measurements on the heat-treated and the reduced samples] of the ion-exchanged and Al-pillared and mixed-metal pillared clays revealed that isomorphous substitution of Al for Fe or Cr did not occur in either the tetrahedral or the octahedral positions. Heat treatment, however, resulted in mixed-metal pillared clays which were active in both acid-catalysed and redox transformations.

Equilibrium and dynamics of acetylene sorption in multiwalled carbon nanotubes

Abstract Multiwalled carbon nanotubes (MWCNT) were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and by adsorption of N 2 and acetylene. The dynamics of acetylene sorption was studied by frequency response spectroscopy. The average tube dimension and the shell number were determined from a statistical evaluation of the TEM images. This value agreed with that obtained from XRD via the Scherrer equation only if a shape factor of 0.49 was used. The diffusion of acetylene in the nanotubes of the MWCNT sample was found to be the rate-controlling step of the sorption process. Relationships between the tube dimensions and the equilibrium and dynamic sorption properties were demonstrated.

An Infrared Study of an Active no Decomposition Catalyst

Abstract NO was adsorbed on Cu-ZSM-5 at temperatures between 173 K δ+ (1900 cm −1 ), NO δ− (1810 cm −1 ) and dimeric or dinitrosyl (NO) 2 (1824 cm −1 and 1730 cm −1 ). Disproportionation of NO at low temperature produced N 2 O and NO 2 . Bands stemming from adsorption of these species were also observed. It was found that an equilibrium exists between the NO δ− and (NO) 2 species bound to reduced Cu sites. The results suggest that the same (NO) 2 species which is a possible intermediate in NO disproportionation at low temperature (≤ 298 K) can be a transient state in NO decomposition at high temperature (> 600 K).

The skeletal isomerization of n-butene over ferrierite catalysts

Abstract The catalytic properties of H-ferrierite zeolites, prepared by hydrothermal and dry-state synthesis, were compared in the skeletal isomerization of 1-butene. The activity was found to be strongly influenced by the presence of extra-framework Al (EFAl) species in the zeolite micropores and by the carbonaceous deposit formed during the reaction. The dynamics of mass transport in the zeolite crystallites were studied by the frequency-response (FR) method using acetylene, propane, n - and i -butane as probe molecules. The selectivity of n -butene conversion showed correlation with the dynamics of the n -butane sorption process. Either the diffusion or the sorption was the rate-controlling slowest step of n -butane mass transport, depending on the amount and the distribution of the EFAl species in the sample. In the catalyst sample, free of EFAl, the transport was found to be controlled by the rate of sorption. At an EFAl content of about 0.5–1.0 EFAl/unit cell the diffusion resistance of the micropores governed the n -butane transport rate.

The effect of adamantane addition on the conversion of n-heptane over H- and Pt/H-zeolites

H- and Pt/H-forms of zeolites Y and mordenite were studied in atmospheric n-heptane (n-C7) hydroconversion at 423–443 K. Adamantane (Ad) additive was found to increase the isomerization and suppress the cracking activity of the H-zeolites. It had minor or no influence on the hydroconversion activity of the Pt/H-forms. Species obtained from Ad adsorbed on zeolites were examined by IR spectroscopy. The Ad-saturated samples (Ad/H-zeolites) were boiled with n-C7 and the liquid phase was analyzed by GC–MS. Results suggested that Ad was activated over the H-zeolites for further reactions via protolysis of its C–H bonds. The Ad and the formed adamantyl carbenium ions (Ad + ) participated in hydride transfer processes. In these processes, the Ad remained unconverted and acted as co-catalyst increasing n-C7 isomerization selectivity. Results suggested that under conditions of n-C7 hydroconversion no or minor amount of Ad + was generated on the Pt/H-zeolite catalysts. Over strong acid mordenite bulky carbocations and Ad compounds were rapidly formed contributing to the decay of the activity in n-C7 conversion.

An FR study of the n- and i-butane diffusion in theta-1, ferrierite and silicalite-1

Abstract In the one-, two-, and three-dimensional (1D, 2D, and 3D) micropore system of theta-1, ferrierite, and silicalite-1, respectively, diffusion to the sorption sites was found to control the rate of propane and butane sorption at 373 K and 133 Pa pressure. The diffusivity of propane (C 3 ) and n -butane ( n -C 4 ) was about the same and much faster than that of the i -butane ( i -C 4 ). In theta-1 and ferrierite, the i -C 4 transport was too slow to be characterized by the frequency–response (FR) method. Ten-ring apertures determine the critical pore dimension of each material. In ferrierite, however, the transport diffusivity of the n -alkanes was about 10 −15 m 2 s −1 , several orders of magnitude smaller than that in theta-1 and silicalite-1. Results suggest that normal alkane diffusion proceeds in the 3D pore system of silicalite-1 and single-file diffusion prevails in the micropores of ferrierite and theta-1.