Side-chain alkylation of toluene with methanol on Cs-exchanged NaY zeolites: effect of Cs loading
- PDF / 401,885 Bytes
- 7 Pages / 595 x 794 pts Page_size
- 68 Downloads / 228 Views
Catalysis Letters Vol. 102, Nos. 1–2, July 2005 ( 2005) DOI: 10.1007/s10562-005-5197-3
Side-chain alkylation of toluene with methanol on Cs-exchanged NaY zeolites: effect of Cs loading A. Borgna, S. Magni, J. Sepu´lveda, C.L. Padro´, and C.R. Apesteguı´ a* Catalysis Science and Engineering Research Group (GICIC), Instituto de Investigaciones en Cata´lisis y Petroquı´mica-INCAPE-(UNL-CONICET), Santiago del Estero 2654, (3000) Santa Fe, Argentina
Received 1 December 2004; accepted 22 February 2005
The side-chain alkylation of toluene with methanol was studied on Cs-exchanged NaY zeolites containing up to 31% Cs (exchange degree, ED, up to 70%). Formation of styrene and ethylbenzene was significant only on Na(Cs)Y zeolites of ED higher than about 40%. Bimolecular side-chain alkylation reaction would require a proper surface geometric configuration of Od)-Cs+ pairs that is achieved only on Cs-rich zeolites. In contrast, the side reaction forming carbon monoxide from methanol increases monotonically with increasing ED because it is essentially controlled by the basicity of the oxygen lattice. KEY WORDS: side-chain alkylations; toluene alkylation; styrene; basic zeolites.
1. Introduction The side-chain alkylation of toluene with methanol for producing a mixture of styrene and ethylbenzene offers economical advantages compared with the conventional homogeneously catalyzed Friedel-Crafts process that uses ethylene and benzene as reactants [1] The reaction is catalyzed by solid bases and has been widely studied, particularly on basic zeolites [2–4]. However, both the reaction mechanism and the active site requirements for enhancing the selectivity toward styrene are not completely understood yet. It has been reported that the side-chain alkylation of toluene with methanol requires a cooperative action of acid/base pairs for efficiently promoting the rate-limiting step in the reaction mechanism [5,6] but other authors suggested that catalyst selectivity is essentially governed by the overall acid–base strength as measured by Sanderson electronegativity [7]. In particular, Palomares et al. [8] studied by in situ infrared spectroscopy the sorption and reaction of toluene and methanol over basic catalysts with the aim of ascertaining the requirements for side chain alkylation.In an attempt to obtain more insight on the active site requirements for the alkylation of toluene with methanol on alkali-exchanged zeolites, we recently explored a new approach for relating the solid surface properties with its catalytic performance based on selective acid–base poisoning [9]. We concluded that active sites involving surface acid–base pairs are required for promoting the rate-limiting step of the reaction mechanism.
* To whom correspondence should be addressed. E-mail: capesteg@fiqus.unl.edu.ar
Although base oxides such as MgO and CaO have been used for side-chain alkylations [10], several studies indicate that the zeolite pores might be indispensable to efficiently catalyze the reaction [11]. The superior catalytic performance shown for a
Data Loading...
