The effect of Al content of zeolite template on the properties and hydrogen storage capacity of zeolite templated carbons

Abstract

We report on the effectiveness of faujasite (Y type) zeolites, with varying Al content, as template for the nanocasting of high surface area zeolite templated carbon (ZTC) via well established chemical vapour deposition routes. The Al content (in the Si/Al ratio range of 1.36–15) was found to have a significant effect on the porosity, nature and hydrogen uptake of the templated carbons. A high Al content zeolite (i.e., zeolite BCR 704, Si/Al = 1.36) performed poorly as nanocast compared to zeolite CBV100 and CBV720 with Si/Al of 2.55 and 15, respectively. Despite comparable porosity amongst the zeolites, zeolite BCR 704 generated low surface area (typically <700 m 2/g) carbons with proportionately larger amounts of carbon with graphitic properties. Zeolite CBV100 generated ZTCs with a wide range of surface area (250–1900 m 2/g), while all carbons generated from zeolite CBV720 had high surface area (1000–1700 m 2/g). In general, surface area decreased at higher CVD temperature which means that the preparation temperature had a lesser influence on the performance of low Al content zeolite such as CBV720. Thus zeolite CBV720 can generate high surface area carbons up to CVD temperature of 1000 °C, while CBV100 and BCR 704 fail to generate high surface area carbons if the CVD temperature is 900 °C or above. The hydrogen uptake of the templated carbons (at −196 °C and 20 bar) closely follows the trend in textural properties, and is in the range 2.3–3.5 wt.% for zeolite CBV720 carbons, 0.6–3.9 wt.% for CBV100 carbons and between 0.01 and 1.6 wt.% for zeolite BCR 704 carbons. The textural and hydrogen uptake data therefore show that, although not used so far, ultrastable Y type (i.e., USY) zeolites such as CBV720 are excellent candidates as templates for high surface area carbons.