Catalysis over Typical Zeolites

whereas it was less than 5% for 2-IPBP. For the DIPB isomers, the narrowest isomer, 4,4 -DIPB, was also formed in high selectivity (ca. 80 %). HZSM-5(50) showed low activity even at 300 °C. 

Catalyst (Si02lAl203) Reaction temp. ro Conv. (%) Product composition Selectivity (%) of IPBP (%) IPBP DIBP 2- 3- 4- Selectivity of DIBP (%) 4.4 - 3.4 - 3.3 -  

The selectivity of an isomer is shown by the percentage in all isomers for each alkylate unless otherwise stated. 

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Catalysis over Typical Zeolites - In the alkylation of naphthalene, a-alkylation occurs in the initial stage because -positions are more reactive than P-positions. However, the (3/a ratio in the product mixture increases with the increase of reaction temperature and time on stream. Figure 8 shows the three reaction paths for producing diisopropylnaphthalene (DIPN) isomers. The reactions are (1) alkylation, (2) isomerization, and (3) transalkylation. Isomerization and transalkylation accompany the rearrangement of isopropyl groups. The zeolite type and reaction conditions, e.g., temperature and time on stream, usually determine the type of reaction path.4... 

Lewis acids immobilized on ionic liquids have been used as the acid catalysts for the alkylation of phenols. The catalytic activities of the immobilized ionic liquids were found to be higher than those for the zeolites. Typically, ionic liquids such as butylmethyUmi-dazoUum halides are treated with AICI3 to give the ionic liquids with halogenoaluminates as the counter anions. They show enhanced Lewis acid character and promote predominantly C-alkylation of phenols over O-alkylation. The alkylation of phenol with dodecene, for example, in the presence of these immobilized ionic liquids results in up to 70% of C-alkylated products (ortho and para products) and 30% of O-alkylated product, comparable to zeolite catalysis (equation 23). The rates of alkylation of phenols are slower than those of arenes due to the complexation of the phenolic group with the Lewis acidic ionic liquids. At higher temperatures conversions of up to 99% could be achieved. 

Typical base-catalysed reactions that occur over alkali metal-exchanged zeolites include dehydrogenations, double bond isomerisations, side-chain alkylation of aromatics, conversion of methyl halides and a range of condensations. The reaction of alcohols over zeolites can be used to determine whether acid or base catalysis predominates. Whereas acid forms of zeolites catalyse dehydrations, leading to alkenes and the products of their subsequent reactions, basic sites catalyse dehydrogenations, leading to aldehydes and ketones. 

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