## 3 Results and Discussion
### Catalytic Performance
[33; 34] showed that the shape-selective effect of zeolites results in linear alkanes being adsorbed in micropores (\"pore mouth\" adsorption) or both ends in adjacent micropores (\"key-lock\" adsorption)[PERSON] [PERSON] et al[PERSON] [34] further pointed out that the adsorption type of n-alkane on the microporous zeolites gradually changed from \"pore mouth\" adsorption to \" key-lock\" adsorption with the increase of reaction temperature[PERSON] Accompanied by an increase in the n-dodecane conversion, the selectivity of the mono-branched isomers decreased gradually (Figure 12a); however, the selectivity of the multi-branched isomers increased gradually (Figure 12b). The selectivity of the mono-branched isomers on the Pt/H-ZS-2 decreases significantly following the increase of n-dodecane conversion, and when the conversion is greater than 81%, the selectivity of multi-branched isomers is higher than that of the other two catalysts. Due to the weak interaction between metal and the carrier and low Pt dispersion, the residence time of isomeric intermediates at the acid sites increase inevitably, which increases the possibility of further branching isomers. At the same time, the ratio of selectivity for mono-branched isomers to multi-branched isomers on different samples is depicted in Figure 12c. Which showed that there is the highest proportion of multi-branched isomers in i-dodecane products on Pt/H-ZS-1 under the same conversion. It is worth noting that the proportion of multi-branched products is relatively low at lower n-dodecane conversion on Pt/H-ZS-2, but when the n-dodecane conversion is higher than 85%, the proportion of multi-branched products is higher than on the Pt/H-ZS-1. This is largely because part of the olefin intermediates cannot be hydrogenated to alkanes at the metal center in time due to the low Pt dispersion on Pt/H-ZS-2 under the high conversion, and further were isomerized to multi-branched i-dodecane. Figure 12: The selectivity of mono-branched isomers (**a**) and multi-branched isomers (**b**) versus n-dodecane conversion on different catalysts; (**c**) the ratio of multi-branched isomers to the mono-branched isomers. (Reaction condition: H\({}_{2}\)/n-dodecane = 750, LHSV = 1.2 h-1, P = 4 MPa)  
In order to study the influence of different acid distribution on the hydroisomerization of long-chain alkanes, the selectivity of cracked by-products and the distribution of several different isomers were analyzed under the condition of n-dodecane conversion of about 90%. The selectivity of cracked products against the carbon numbers distribution is plotted in Figure 13. On different catalysts, most of the cracked products account for a large proportion of linear alkanes, and the proportion of cracked isomers in the cracked products of the same carbon number increases with the increase of carbon number, which follow the type C \(\beta\)--cracking [35]. The distribution of cracked by-products is similar on Pt/H-ZS-1 and Pt/H-ZS-2 because of their similar acidic distribution, while the Pt/H-ZN-1 shows the highest cracking selectivity due to the more B acidity and L acid content of the carrier. Under the condition that the conversion rate of n-dodecane is about 90%, the distribution of several different i-dodecanes is analyzed, as shown in Table 4, the main branches of the mono-branched isomers are methyl. An increase in the reaction temperature corresponds to weak B acid sites and less Pt sites of the Pt/H-ZS-2 leads to the enhancement of key-lock adsorption. Further, the selectivity of the intermediate branched isomers was improved and the second cracked reaction was inhibited. As a result, Pt/H-ZS-2 exhibits the highest selectivity for 4-6-Methylundecane and 2,4-9-DimethylInonane. The secondary cracking reaction of Pt/H-ZN-1 is intensified by its strong and high B acid content, which shows the lowest selectivity of the multi-branched i-dodecanes.