1. Introduction Recently, we have developed a method for preparing the CHA-type zeolite with the distribution of framework Al atoms controlled, i.e., the proportion of Q4(2Al)/Q4(1Al) ratio, where Q4(nAl) is Si(OSi)4-n(OAl)n. In this work, the impact of Al distribution in the Cu-exchanged CHA-type zeolite on the catalytic performance in CH4 conversion was investigated. 2. Experimental The CHA-type aluminosilicate zeolites with different proportions of Q4(2Al)/Q4(1Al) ratios were synthesized from the different starting materials including fumed silica, aluminum hydroxide, and the high-silica type FAU-type zeolite (HSZ-350HUA , Si/Al = 7.3), with their proportions varied. Cu-ion exchange was carried out using Cu(NO3)23H2O. The CH4 conversion was performed in a fixed bed reactor. The flow rates of the reactants were CH4/O2/Ar = 16/4/5 (SCCM). 3. Results and discussion The 29Si MAS NMR spectra clearly showed that thus obtained CHA-type zeolites had different Al distributions depending on the proportion of the FAU-type zeolite as the starting material. The use of the high-silica-type FAU-type zeolite with a high proportion led to the high proportion of Q4(1Al). Here, representative catalysts were designated as “Q4(1Al)-rich” and “Q4(2Al)-rich”, respectively. The Si/Al ratios of Q4(1Al)-rich and Q4(2Al)-rich were 3.4 and 4.4, respectively, and the Cu contents for both catalysts were almost similar, ca. 0.8 wt%. Their catalytic activities in CH4 conversion were investigated. Both catalysts showed similar CH4 conversion. However, there was a significant difference in the products selectivities. The yield of CO2 on Q4(1Al)-rich catalyst was higher than that on Q4(2Al)-rich. The yields of target products, CH3OH, C2H6 and C2H4 on Q4(2Al)-rich were higher than those on Q4(1Al)-rich. At 500 °C, for the Q4(2Al)-rich and Q4(1Al)-rich catalysts, 0.2 and 0.1 % of CH3OH yields were achieved, respectively. These results clearly suggest that the Al distribution affected the catalytic performance; Q4(2Al)-rich catalysts are advantageous for the formation of “reactive Cu species, i.e., binuclear Cu-O-Cu” for CH4 activation.

Effect of framework Al location in metal cation-exchanged zeolites on methane conversion

2019 Spring National Meeting

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