Effect of Loaded Alkali Metals on the Structural, Basicity and Catalytic Activity of Zeolite Beta

Abstract

Zeolit beta diubahsuai dengan memasukkan logam alkali (Na,K,Cs) kepada zeolit melalui kaedah pengisitepuan basah. Kehadiran logam alkali ini telah menurunkan kehabluran dan luas permukaan BET zeolit beta menurut keputusan pencirian sampel melalui XRD, IR dan penjerapan nitrogen. Bingkaian zeolit musnah pada muatan Na dan K, > 8%w/w. Sebaliknya kepekatan tapak bes meningkat seperti yang dibuktikan daripada peningkatan penjerapan CO₂ dengan kaedah TPD–CO₂ dengan peningkatan amaun muatan logam. Aktiviti mangkin sampel yang diubahsuai diuji dalam tindak balas nyahhidratan–nyahhidrogenan sikloheksanol. Kepilihan sikloheksanon yang terhasil pada tapak bes zeolit beta meningkat dengan peningkatan kebesan, yang seterusnya menahan kepilihan terhadap sikloheksena terhasil di tapak asid zeolit. Namun, sikloheksena masih lagi merupakan hasil utama disebabkan sifat asid zeolit beta yang lebih dominan. Nisbah sikloheksena kepada sikloheksanon berubah–ubah dengan peningkatan muatan logam alkali. Kata kunci: zeolit Beta berbes, logam alkali, kebesan, nyahhidratan-nyahhidrogenan sikloheksano Zeolite Beta was modified by incorporation of an alkali metal (Na, K, Cs) through wet impregnation method. The incorporation of the base guests has reduced the crystallinity and BET surface area of zeolite Beta, as evidence by XRD, IR and nitrogen adsorption characterizations. The framework structure was totally collapsed at > 8%w/w loading of Na and K. Nevertheless, the concentration of base sites (basicity) was enhanced as evidence by the increase in the amount of desorbed CO₂ in TPD–CO₂ as the amount of metal loading increases. The catalytic activity of the modified samples was tested in dehydration–dehydrogenation of cyclohexanol. Selectivity of cyclohexanone that is produced on base sites of zeolite Beta increased with the increase in the basicity, consequently suppressed the selectivity of cyclohexene produced at acidic sites. Cyclohexene was obtained as the dominant product due to the dominant acidic properties of zeolite Beta. The ratio of cyclohexene to cyclohexanone varies with the increase in the metal loading. Key words: Base zeolite Beta, alkali metal, basicity, dehydration-dehydrogenation of cyclohexanol