Spectroscopic and microscopic studies of Co, Ce, and Pd containing gamma-alumina as catalysts for cyclohexene oxidation

Abstract

The oxidation of cyclohexene belongs to the most important reactions in organic chemistry and leads to the production of the precursors for surfactants, polymers, agrochemicals, and drugs. So far, however, due to a complex reaction mechanism, it was hard to find the catalyst of satisfactory properties.Attractive catalysts in this reaction could be sonochemically prepared Co, Ce, and Pd containing γ-Al2O3, which is the object of the undertaken research. What is more, this combination of metals in the oxide system has not been studied. The analysis of catalytic performance indicated that all studied catalysts were active in the catalytic oxidation of cyclohexene. For metal-containing alumina (Me=Co, Ce, Pd), the conversion of cyclohexene was 61–84%. The best catalyst was Co5Ce5/γ-Al2O3s, prepared via the sonochemically-assisted procedure.It was also shown that the application of ultrasonic irradiation during the preparation of samples enhanced metal distribution over alumina support, resulted in smaller crystallites of prepared materials, and caused higher surface area with simultaneous smaller both pore size and pore volume in comparison with counterparts prepared via the standard procedure. XRD, Ra, and DR..-UV–vis spectroscopies indicated the coexistence of Co as Co3O4 and CoAl2O4 spinel, however, Ce was found in the form of CeO2. The addition of Pd to Co/γ-Al2O3 did not influence the status of cobalt.