Tuning 1-hexene adsorption via ion-exchange of binderless
zeolite NaX
To finetune the 1-hexene adsorption performance, we further modified the
synthesized binderless zeolite NaX pellets by post-synthesis
ion-exchange with a series of metal nitrate solutions. The chemical
compositions of all ion-exchanged zeolite X samples are listed in Table
S1. The XRD patterns in Figure 8 confirm that all ion-exchanged
binderless samples share characteristic FAU topology. However, decrease
in peak intensity due to crystallinity loss can be observed for all
ion-exchanged samples. Similar findings have been reported
previously.57 Among these ion-exchanged samples,
Mg-NaX and Ca-NaX present comparable XRD peak intensity as the parent
NaX sample with relative crystallinity of 89.4 % (Mg-NaX) and 81.3 %
(Ca-NaX), while Co-NaX, Cu-NaX, Zn-NaX and Ag-NaX exhibit crystallinity
degradation of about 40 %, with relative crystallinity of 62.4 %
(Co-NaX), 57.6 % (Cu-NaX), 61.5 % (Zn-NaX) and 60.3 % (Ag-NaX).
Introduction of Co2+, Ni2+,
Cu2+, Zn2+ and Ag+into the parent zeolite X decreases the BET specific surface area and
overall pore volume (see Table S3). This is primarily caused by the
degradation in crystallinity during ion-exchange, suggested by the XRD
results. In contrast, incorporation of divalent Mg2+and Ca2+ into zeolite X structure generates more free
space when keeping the overall framework charge being balanced, leading
to increased BET specific surface area and pore
volume.58 In addition, Mg-NaX and Ca-NaX show
comparable crystallinity to that of the parent NaX, and decrease in
molecular weight (see Table S1 for chemical compositions of different
samples) also accounts for the change in pore structure analysis results
on a weight basis.