Karolina A. Tarach

Catalytic dehydration of ethanol over hierarchical ZSM-5 zeolites: studies of their acidity and porosity properties

The catalytic activity of novel micro/mesoporous ZSM-5 in the dehydration process of alcohols has been studied with respect to their acidity and porosity. Samples characterized by similar Si/Al ratios in the range between 23 and 36 were chosen to ensure the ability to properly monitor the changes in catalytic performance related to the concentration of acid sites, as well as their accessibility and strength. Special attention has been paid to porosity studies involving low-temperature nitrogen sorption and the quasi-equilibrated temperature programmed desorption of hydrocarbons. Thus, the wide range of materials from typically microporous ZSM-5 to micro/mesoporous analogues obtained by different methods, but presenting many similar properties, allowed us to investigate the influence of porosity character on catalytic performance. Both the acidity and porosity properties, which were significantly perturbed by various synthesis and modification strategies, were clearly reflected in the catalytic performance of hierarchical zeolites, described as volcano curve dependence.

Acidity and accessibility studies of desilicated ZSM-5 zeolites in terms of their effectiveness as catalysts in acid-catalyzed cracking processes

The structural, textural and acidic characteristics of hierarchical ZSM-5 (Si/Al = 18–32), obtained with two desilication approaches, and the effect of these treatments on the reactivity in various cracking reactions of variable feedstock size and severity have been investigated. Emphasis is given to understanding the accessibility of acid sites; this was investigated by textural analysis, FTIR probe molecules (pyridine, trimethylacetonitrile and 2,4,6-trimethylpyridine) and reactions involving n-decane, 1,3,5-triisopropylbenzene (TIPB), and low and high-density polyethylene, LDPE and HDPE, respectively. Higher surface areas and a narrower pore size distribution were obtained for NaOHT both parameters are linearly dependent on the pivalonitrile and collidine accessibility factors, for LDPE and HDPE. The T5% for HDPE is more influenced by the accessibility factors than it is for the LDPE. This is interpreted to be the result of the branching degree of HDPE and LDPE; linear HDPE is more sensitive to the enhanced number of pore mouths of ZSM-5 channels on the mesopores. At high conversion, the influence on the T50% of the accessibility factors for HDPE and LDPE is weaker, suggesting that the cracking at this stage involves intermediate molecules of smaller size with fewer diffusional limitations. With respect to our own prior work, the chosen zeolite and the cracking of polyolefins gave more pronounced differences for the hierarchical ZSM-5.

Water thermoporosimetry as a tool of characterization of the textural parameters of mesoporous materials

Water thermoporosimetry (TPM) is a powerful method for studying the properties of porous materials, devoted especially for investigation of the samples that can be destroyed in drying process. However, this method is not very popular and relatively rarely used because of problems with proper measurement procedure and choosing correct equation for the result interpretation. This report focused on refinement of general experimental protocols for water TPM. For the first time, the role of various parameters on the TPM outcomes was deeply investigated and simple and fast experimental mode was proposed. Additionally, based on the series of mesoporous silica SBA-15, the calibration procedure was employed and the reliable calibration equations were established.

Ag-loaded zeolites Y and USY as catalysts for selective ammonia oxidation

IR spectroscopic studies of NH3 and CO adsorption were applied to establish the status of Ag0 and Ag+ in silver loaded zeolites Y and USY. The nature of the silver particles and ions and their dispersion were found to be influenced by the type of support. Application of zeolite USY as support allowed to operate such catalysts at low temperatures with high selectivity to nitrogen (95%). Zeolite USY as support guaranteed a high concentration of uniformly dispersed metallic silver species and Ag+ cations with strong electron acceptor properties. The silver species of defined nature together with the highly acidic centres in AgUSY protected NH4+ ions against oxidation thus high selectivity to nitrogen was observed.

Ethylene formation by dehydration of ethanol over medium pore zeolites

In this work, the role of pore arrangement of 10-ring zeolites ZSM-5, TNU-9 and IM-5 on their catalytic properties in ethanol transformation were investigated. Among all the studied catalysts, the zeolite IM-5, characterized by limited 3-dimensionality, presented the highest conversion of ethanol and the highest yields of diethyl ether (DEE) and ethylene. The least active and selective to ethylene and C3+ products was zeolite TNU-9 with the largest cavities formed on the intersection of 10-ring channels. The catalysts varied, however, in lifetime, and their deactivation followed the order: IM-5>TNU-9>ZSM-5. The processes taking place in the microporous zeolite environment were tracked by IR spectroscopy and analysed by the 2D correlation analysis (2D COS) allowing for an insight into the nature of chemisorbed adducts and transition products of the reaction. The cage dimension was found as a decisive factor influencing the tendency for coke deposition, herein identified as polymethylated benzenes, mainly 1,2,4-trimethyl-benzene.