3
0
S. Ogo et al. / Journal of Catalysis 296 (2012) 24–30
other hand, Sr-HAP catalysts with higher Sr/P ratios (>1.67) have a
larger number of relatively strong basic sites. Although the XRD
pattern of Sr-HAP (1.70) showed a single apatite phase, the highly
dispersed SrO species might be formed on the surface [3] and
might act as relatively strong basic active sites, together with the
bulk Sr/P molar ratios. Both relatively strong acidic and basic site
densities of the Sr-HAP catalysts increased with the increase in
the Sr/P molar ratio, although the basic site density was signifi-
cantly higher than the acidic site density. The rate-determining
step in 1-butanol formation from ethanol is postulated to be aldol
condensation, including the condensation process itself and the
formation of two aldehyde adsorbates on neighboring basic sites
just before condensation. Catalysts with higher Sr/P molar ratios
had higher densities of relatively strong basic sites, which could
explain why Sr-HAP catalysts with higher Sr/P molar ratios show
higher catalytic activity and 1-butanol selectivity in the catalytic
conversion of ethanol.
2
catalysts’ active sites. However, a SrO/SiO catalyst showed low
catalytic activity and 1-butanol selectivity (Table S6). These results
suggested that SrO species alone have too little activity, but
dispersed SrO species on Sr-HAP might play a significant role in
1
-butanol formation from ethanol. Moreover, surface hydrogen
species would increase with the increase in dehydrogenated adsor-
bates, such as aldehyde and enol species, and this would lead to
acceleration of the hydrogenation rate of aldehyde species and
suppression of the formation of unsaturated by-products and suc-
cessive reaction products. The fact that Sr-HAP catalysts with high-
er Sr/P ratios exhibited higher catalytic activity and selectivity for
Acknowledgments
We acknowledge support from Sangi Co. Ltd. Part of this study
was supported by the Cooperative Research Program of the Catal-
ysis Research Center, Hokkaido University (Grant 2010-B-2002).
We thank Professor Tsuneji Sano, Graduate School of Engineering,
Hiroshima University, for his great technical assistance and helpful
suggestions for measurement of the FT-IR spectrum of pyridine ad-
sorbed on the catalyst.
1
-butanol could be ascribed to their catalytic properties for the for-
mation of ethanol dehydrogenated adsorbates and hydrogen
adsorbates.
+
To clarify the effect of Na ions on the catalytic properties of
Sr-HAP catalysts, we also prepared Sr-HAP-NH
3
(1.57) and
(1.71) catalysts without Na ions. The Sr-HAP-NH
1.57) and Sr-HAP-NH (1.71) showed almost the same Sr/P molar
+
Sr-HAP-NH
3
3
(
3
ratios (1.57 and 1.71) and XRD pattern as those of Sr-HAP (1.58)
and Sr-HAP (1.70), respectively. As shown in Table 3 and Table
Appendix A. Supplementary material
S6, the Sr-HAP-NH
but selectivity different from those of the Sr-HAP (1.58). The
Sr-HAP-NH (1.57) catalyst had relatively high selectivities toward
3
(1.57) showed catalytic activity similar to
3
ethylene and diethyl ether, which were due to acid catalysis,
whereas ethylene and diethyl ether did not form over the Sr-HAP
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