Acidic zeolites are attractive alkylation catalysts due to their high activity, stability, and adjustable shape-selectivity. An excellent alkylation catalyst should have two main characteristics: shape selectivity towards desirable products and catalysts stability against coke, and these characteristics can be improved by introducing chemical additives into zeolites. The use of lanthanum (La) as an additive has been extensively implemented in the petrochemical industry. Despite the wide usage of La as an additive in zeolites, its exact role is still a matter of extensive investigation. This work investigates the effects of La incorporation in H-MOR and focuses on the shape selectivity and catalysts' stability against coking in alkylating toluene and isopropanol. Lanthanum-doped mordenite (La-MOR) were synthesized via incipient wetness impregnation with varying La(NO₃)₃ concentrations, then calcined. The alkylation reactions were carried out in a liquid-phase batch reactor and gas-phase continuous flow reactor at varying catalyst mass and reactants' concentrations. Characterization techniques, including IPA-TPD, BET, XRD, TGA, FTIR, and ¹³C-NMR, were performed to understand the effect of La on MOR. In alkylating toluene with isopropanol, La incorporation inside MOR zeolite was found to enhance para-selectivity while suppressing orto-selectivity. The presence of La restricts the zeolite pore, favoring para-isomer, which is the kinetically less bulky alkylated product. La addition in MOR also improves the catalyst stability against coking by decreasing the reaction deactivation coefficient. La-MOR produces less coke than H-MOR. La-MOR coke appears to burn off more easily than the H-MOR coke, indicated by lower combustion temperature. This suggests that either the nature of coke is different or La facilitates the oxidation of coke. ¹³C-NMR shows that La-MOR coke has more tertiary carbon than H-MOR. This result potentially explains the difference in the easiness of the coke-burning process, which may be due to the role of La in improving hydride transfer.

Nabihan Abdul Rahman

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