Effect of the template ion exchange behaviors of chromium into FSM-16 on the oxidative dehydrogenation of isobutane

Abstract

The template ion exchange of chromium cations into FSM-16 (#16 Folded Sheets Mesoporous Materials) for 247 h resulted in a 2.89 wt % incorporation of those cations into the FSM-16, although only a 0.3 wt % incorporation had previously been reported. The XRD pattern of the resultant solid (Cr-FSM-16) showed that the hexagonal structure characteristic of FSM-16 remained after the 2.89 wt % incorporation of chromium cations. XPS could be used to detect the Cr 3+ and Cr 6+ species on the surface of Cr-FSM-16. A pre-edge peak that was due to a tetrahedrally coordinated Cr 6+ species was confirmed in the XANES spectrum of the Cr-FSM-16, which showed that the coordination state around some Cr species was similar to that around the Si species in FSM-16. With the increase in the amount of chromium cations in FSM-16, its catalytic activity and stability during the oxidative dehydrogenation of isobutane were evidently improved.

Introduction of a Small Amount of Chromium to Enhance the Catalytic Performance of SBA-15 for the Oxidative Dehydrogenation of Isobutane to Isobutene

“…In contrast, in the present study, a trade-off relationship was observed between the selectivity for CO and that for C 3 species, probably owing to the suppressed conversion of CO to CO 2 . In the present study, maximum isobutene yields of more than 15% were detected using Cr-SBA-15 (Si/Cr = 100 and 50) during the initial 2.0 and 3.25 h on-stream, respectively, under the standard reaction conditions used in our previous studies (Sugiyama et al, 2013(Sugiyama et al, , 2015Ehiro et al, 2015Ehiro et al, , 2016aEhiro et al, , 2016bEhiro et al, , 2017, in which the maximum isobutene yield was less than 8%. Additional activity testing using Cr-SBA-15 (Si/Cr = 50) also showed enhanced isobutene yields (16.8 and 15.3% after 0.75 and 2.0 h on-stream, respectively), which were comparable to the above yields.…”

“…With respect to the structural factors, a specific surface area of greater than 1,600 m 2 /g should be a main contributor to enhanced activity. The growth of micropores in Cr-SBA-15 was detected in the present study, but this feature has not been observed in either FSM-16 or MCM-41 when doped with chromium (Sugiyama et al, 2013(Sugiyama et al, , 2015Ehiro et al, 2015Ehiro et al, , 2016aEhiro et al, , 2016bEhiro et al, , 2017. Therefore, this structural factor is unique to Cr-SBA-15 and results in increased activity.…”

“…In preliminary experiments, various preparation methods, such as template-ion exchange (Yonemitsu et al, 1997), incipient wetness impregnation (Wang et al, 2009), and direct synthesis (Grieken et al, 2009) were used to prepare chromium-added SBA-15. It should be noted that chromium could not be introduced into SBA-15 using template-ion exchange, although previous reports have noted that this method is suitable for introducing chromium into the frameworks of both FSM-16 and MCM-41 (Ehiro et al, 2015(Ehiro et al, , 2016a. The catalytic activity of Cr-SBA-15 prepared via incipient wetness impregnation (isobutene yield = 7.6%) was similar to those of FSM-16 and MCM-41 containing chromium.…”

“…These are known as active catalysts for ODH, in this case, their use resulted in an isobutene yield of less than 2% at reaction temperatures below 723 K (Furukawa et al, 2011). However, employing the template-ion exchange method (Yonemitsu et al, 1997) to introduce chromium cations into various mesoporous silicas, such as FSM-16 (Sugiyama et al, 2013(Sugiyama et al, , 2015Ehiro et al, 2015) and MCM-41 (Ehiro et al, 2016a), significantly improved the isobutene yield to 8%. Relatively greater isobutene yields of 6-8% have been obtained by several methods: acid treatment of MCM-41, aluminum-doping of MCM-41 (Ehiro et al, 2016b) prepared via the template-ion exchange method, and the use of calcium phosphates with or without impregnated chromium oxide (Ehiro et al, 2017).…”

Effect of Introduction of Trace Amount of Chromium Species in Improving Catalytic Performance of MCM-48 in Oxidative Dehydrogenation of Isobutane

“…Therefore, introduction of the chromium species into various mesoporous silicas and its effect on the ODH of isobutane has remained a research focus in our laboratory, and we found that the catalyst performance was enhanced (Sugiyama et al, 2015). For example, the chromium species was either introduced or impregnated into various mesoporous silica catalysts possessing a uniform hexagonal structure such as FSM-16 (Sugiyama et al, 2013(Sugiyama et al, , 2015Ehiro et al, 2015) and MCM-41 (Ehiro et al, 2016a(Ehiro et al, , 2016b and great improvement in the yield of isobutene was recorded (≈8% at 723 K). Recently, a similar enhancement was observed during the ODH of isobutane using SBA-15 when a trace amount of chromium was introduced (Kato et al, 2018).…”