Preparation and characterization of molybdenum sulfide supported on β-zeolites obtained from [Mo 3S 4(H 2O) 9] 4+ precursor

Abstract

In this paper, we report an alternative procedure of cation exchange to introduce higher amount of [Mo 3S 4(H 2O) 9] 4+ in β-zeolites than as reported for various zeolites (∼2 wt.%). The parent β-zeolite (Si/Al = 13.8) was partially dealuminated with a nitric acid treatment (Si/Al = 15.0 and 18.7). The three zeolites of various acidities were used as supports. The addition of ammonia during the cation exchange procedure allowed us to double the Mo loadings (4.5 wt.%) even with the most dealuminated zeolite. The acidity of the zeolitic host was restored after exchange through a thermal treatment at 350 °C under Ar. Characterizations of the Mo/β catalysts by XRD, BET and EXAFS revealed that the structures of the zeolites and that of [Mo 3S 4(H 2O) 9] 4+ were preserved during ion-exchange procedure. After the thermal treatment at 350 °C, UV–visible spectroscopy, EXAFS and TEM showed that the [Mo 3 IVS 4(H 2O) 9] 4+ was decomposed leading to Mo IVS 2 and a Mo VIO x species probably grafted onto the zeolite surface. Whatever the exchange conditions, in presence or in absence of ammonia, molybdenum was mainly located on the external surface of the zeolite grains and a small fraction was inside the porosity as indicated by the TEM study.