Properties of supports
Small angle XRD patterns of various supports are displayed in Fig. S1.
It showed that all samples present a sharp peak ranged from
0.5o to 1o, which is an indicative
of (110) reflection and a 3D cubic meso-structure with Im3m space
group. Meanwhile, a poor-resolved shoulder at about
1.2o should be assigned to (200)
reflection.[22] It can deduce that SBA-16 silica
is successfully synthesized and the structural order degree of SBA-16
material can be maintained after incorporation of Al and Ti species.
N2 adsorption–desorption isotherms of different
supports are shown in Fig. S2. The textural properties of different
supports, determined from N2 adsorption–desorption
isotherms, are displayed in Table 1. The BET surface area and pore
volume of SBA-16 pure silica are the highest of 975.7
m2·g-1 and 1.38
cm3·g-1, respectively. The pore size
of SBA-16 pure silica is lower than that of Al-Ti-SBA-16 composites
except AT-0 support, which may be resulted from the longer calcination
time for AT-7.5, AT-10, AT-5 and AT-2.5 supports and further generation
of intergranular pores. Moreover, the cubic unit cell parameters
a0 of Al-Ti-SBA-16 composites modified by duplex metals
are higher than those of SBA-16 pure silica and only Al or Ti modified
SBA-16 materials. The mesopores void fractions εmes of
Al-Ti-SBA-16 composites ranged from 0.66 to 0.69 are lower than that of
SBA-16 material. The diameter of the spherical cavities
Dme for AT-2.5 support presents the highest value of
3.80 nm. The wall thickness hw of Al-Ti-SBA-16
composites composed of both Al and Ti atoms are higher than other
materials. Above all, the incorporation of Al and Ti species through the
stepwise method can protect the textural properties and maintain the
highly ordered degree of SBA-16 silica.
Table 1 Textural properties of serial supports.