An Integrated Catalytic and Transient Study of Sulfated Zirconias: Investigation of the Reaction Mechanism and the Role of Acidic Sites in n‐Butane Isomerization

Abstract

The transient temporal analysis of products (TAP) pulse method has been applied to investigate the isomerization of n‐butane on sulfated zirconias at very low pressure. By combining these results with findings from XRD, XPS, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), temperature‐programmed desorption (TPD), and catalytic studies at atmospheric pressure, a wide range of pressure conditions can be accessed to study the influence of surface sulfate groups on the isomerization activity and the mechanism of this reaction. The catalytic activity of powder catalysts has been correlated to the surface site density of sulfates, with pyrosulfate structures playing a major role in the initiation of the reaction. The complex interplay between sulfate‐free and sulfate‐covered zirconia surfaces for the adsorption of alkanes has been investigated in detail, with TAP pulse experiments showing a monomolecular reaction pathway at low n‐butane partial pressures. Moreover, TAP pulse experiments have allowed detection of the reaction products of this initiation process, including butene and water, and have shown their influence on the deactivation of sulfated zirconias. Heats of adsorption have been calculated from the TAP pulse experiments.

In‐situ characterization of aqueous‐based hafnium oxide hydroxide sulfate thin films

“…The surface acid properties of sulfated metal oxides are known to drive a wide range of catalytic reactions . In this study, we have characterized the surface chemistry of dehydrated HafSOx surface by performing D 2 O TPD experiments.…”

“… Sulfated zirconia, an isoelectronic analog of HafSOx, exhibits exceptional activity in the isomerization of n‐alkanes. The roles of surface acidity, metal oxide composition, and method of preparation in controlling the acid‐catalyzed reaction mechanisms of the isomerization processes are still under investigation. It has been proposed that the application of surface‐science techniques to investigate the adsorption‐desorption properties from model thin‐film systems will provide additional insights on catalytic mechanisms and material properties for these complex systems.…”

Determination of Extinction Coefficients for Describing Gas Adsorption on Heterogeneous Catalysts Using In-Situ DRIFT Spectroscopy

“…The change in the characteristic sulfate band at 1400 cm −1 was used to describe the SZ and n-butane interaction as well as to determine the extinction coefficients. The band at 1400 cm −1 can be assigned to the stretching vibration of the S=O bond, which is associated in the literature with a disulfate structure on the surface of the catalyst [12,14]. It has a double-band structure with a maximum at 1400 cm −1 and a shoulder at 1375 cm −1 with lower intensity.…”

“…This system has already been widely studied due to the good catalytic properties of sulfated zirconia for the skeletal isomerization of small alkanes at low temperatures. Examples of this are the investigations of Wrabetz [10], Li [11], Breitkopf [12], and Gonzáles [13], which were carried out with microcalorimetry. In these investigations, the surface of the activated sulfated zirconia was characterized and the number of active sites and sorption heats were determined.…”

Simulation of the Frequency Response Analysis of Gas Diffusion in Zeolites by Means of Computational Fluid Dynamics

“…The characterization of the gas diffusion properties of porous materials, such as zeolites, holds significant relevance across a broad spectrum of applications: from characterizing gas-specific adsorbents to catalyst design [1,2]. Various time-resolved characterization methods are available, including the temporal analysis of products (TAP) [3][4][5], electrochemical impedance spectroscopy (EIS) [6,7], or frequency response (FR) [2,8].…”