Acidity properties of Ni-exchanged mordenites prepared with and without microwaves

• Published in: Applied catalysis. A, General Vol. 368; no. 1; pp. 163 - 169
• Main Authors: Bergadà, Olga, Boix, Estefanía, Salagre, Pilar, Cesteros, Yolanda, Medina, Francisco, Sueiras, Jesús E.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 31.10.2009; Elsevier
• Subjects: Acidity; Catalysis; Chemistry; Exact sciences and technology; General and physical chemistry; Ion-exchange; Microwaves; Mordenite; Ni 2+ exchange; Styrene oxide isomerization; Styrene oxide ring-opening; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Zeolites: preparations and properties; Mordenite; Styrene oxide isomerization; Acidity; Ni 2+ exchange; Styrene oxide ring-opening; Microwaves; Heat treatment; Nitrogen heterocycle; Acidic site; Microwave; Oxides; Liquid phase; Molecular sieve; Ring cleavage; Characterization; Six membered ring; Microwave irradiation; Ni; Ion exchange; Lewis acid; Catalytic reaction; Hydrocarbon; Isomerization; Transition metal; Zeolite; Infrared spectrometry; Ammonia; Heterogeneous catalysis; Pyridine; Heating; Styrene; Benzenic compound; Nickel; exchange
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2009.08.028

Microwaves allowed us to obtain, after one exchange (M9), similar Ni 2+ exchange (47%) than conventional heating but much faster. Making a thermal treatment under microwaves between two exchanges made also under microwaves, the exchanged Ni 2+ increased to 84% (M15). Microwaves, especially at longer treatment times, resulted in new weak Lewis acid sites which were not present in the samples conventionally exchanged (M13). We prepared several Ni,Na-mordenites by ion-exchange of commercial Na-mordenite in the liquid phase under microwaves irradiation and by conventional heating for comparison. After one exchange at 333 K, similar amounts of exchanged Ni 2+ (around 47%) were achieved with and without microwaves but faster under microwave irradiation. Making an intermediate thermal treatment under microwaves between two exchanges, also made under microwaves, the exchanged Ni 2+ increased up to 84%. Interestingly, microwaves strongly affect the acidity of the exchanged samples since they showed the appearance of new weak acid sites, which increased as longer the microwaves treatment was (NH 3-TPD). This agrees with the higher amounts of Lewis acid centres observed by adsorbed pyridine FTIR for these samples. These new sites were not observed for the conventional exchanged sample. From these results, we believe that microwaves could interact with nickel cations inducing the formation of weak-acid hydrolised nickel species [Ni(OH)] + for the microwaved samples. These acid characterization results were confirmed by testing several of these Ni,Na-mordenites in two reactions catalysed by different acid sites.