Synthesis gas conversion utilizing mixed catalyst composed of CO reducing catalyst and solid acid. Part 5. Effect of acidic properties of zeolite on product distribution.:Effect of Acidic Properties of Zeolite on Product Distribution
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Synthesis gas conversion on hybrid catalysts composed of a physical mixture of methanol synthesis catalyst (Pd/SiO2) and acid treated or steam treated mordenites, was studied. Acidic properties of the zeolites which are summarized in Table 1 show that aluminium contents and acidities of acid treated mordenite, DAM-1 and DAM-2, are much smaller than those of their parent mordenite, H-M. This fact indicates that aluminium was extracted from H-M by the acid treatment to destroy mainly Brönsted acid site. Also, the treatment caused an increase in the fraction of strong acid site (fraction of acid site which holds ammonia up to 300°C or above). In contrast, remarkable amount of acid site was destroyed by steam treatment 450°C, 2h) supposedly by hydrolysis whereas little aluminium was extracted. For instance, the aluminium content of St. DAM-1 is on the same level of that of DAM-1 but the acidity of St. DAM-1 is one third of that of DAM-1. IR spectra of adsorbed pyridine on zeolites (Figs. 3-6) show that hydrogen bonded pyridine (H-acid) was increased by either the acid treatment or the steam treatment. The H-acid site, on which ammonia is not chemisorbed, is most favorably attributed to a silanol group which is formed by the hydrolysis of the structure of Al-O-Si or Si-O-Si.Results of synthesis gas conversion on the hybrid catalysts containing the modified mordenites (Table 3) is characterized by the products being mostly composed of light paraffins and polymethylbenzenes. While the selectivities to aromatic hydrocarbons plus coke on the hybrid catalyst are on the same level (ca. 35%) for all catalysts tested, the selectivities to coke on the hybrid catalyst containing DAM-1 and especially St. DAM-1 are much smaller than those on the hybrid catalyst containing H-M or DAM-2 (Fig. 9). The fact indicates that aromatic hydrocarbons are formed simultaneously with aliphatic hydrocarbons then they are converted successively to coke. The reductions of coke formation on zeolites by either the acid treatment or the steam treatment are most likely attributed to the reduction of the affinity of the zeolite for aromatic hydrocarbons (Fig. 8), which are caused by the decrease in the acidity and the increase in the hydroxyl group.
- 公益社団法人 石油学会の論文
公益社団法人 石油学会 | 論文
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