Roles of Carrier Gases on Deactivation and Coking in Zeolite Beta during Cumene Disproportionation

• Published in: Journal of catalysis Vol. 163; no. 2; pp. 436 - 446
• Main Authors: Chen, Wen-Hua, Pradhan, Ajit, Jong, Sung-Jeng, Lee, Ting-Yueh, Wang, Ikai, Tsai, Tseng-Chang, Liu, Shang-Bin
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.10.1996; Elsevier
• Subjects: Catalysis; Catalysts: preparations and properties; Chemistry; Exact sciences and technology; General and physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Disproportionation; Deactivation; Hydrocarbon; NMR spectrometry; Zeolite; Experimental study; Coke deposition; Molecular sieve; Heterogeneous catalysis; Reaction mechanism; Benzenic compound; Cumene; Carrier gas
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1006/jcat.1996.0345

The influence of carrier gases (N2, H2, He, and CO2) on the catalytic activity, stability, and coke formation in zeolite beta during cumene disproportionation reaction is discussed. The reaction intermediates as well as the carbonaceous residues were characterized by13C NMR spectroscopy under proton cross-polarization and magic-angle spinning and by thermogravimetric method. The effects of carrier gas dilution on coke formation, catalyst deactivation, and product shape selectivity have also been examined by varying carrier gas (N2) to reactant molar ratios (0.2–20). The amount of total coke decreases linearly with increasing N2/cumene ratios above a value near 2. It is also found that the coke induced shape selectivity is notable only at extreme dilution. In the presence of various carrier gases, a notable decrease in catalytic activity has been found to obey the order N2>H2>He>CO2, whereas a reverse order was observed for the catalytic stability. Moreover, the amount of coke deposit is found to decrease linearly with the kinetic diameter of the carrier gases. Hence, the incorporation of carrier gases resulted in a decrease in the amount of coke deposition which is mainly due to the transport of coke precursors and less bulky carbonaceous compounds (soft coke). Similarly, as proposed by the transition complex solvation model, the carrier gas molecules stabilize the biphenyl alkane reaction intermediates by van der Walls interactions and prevent them from further dissociation into product molecules. With the exception of H2, the combination of the carrier gas transport effect and transition complex solvation model is used to describe the observed trends in the activity and stability of the catalyst.