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.