Selective Catalytic Oxidation of Toluene to Benzaldehyde: Effect of Aging Time and Calcination Temperature Using CuxZnyO Mixed Metal Oxide Nanoparticles

Oxidation is an important organic transformation, and several catalysts have been reported for this conversion. In this study, we report the synthesis of mixed metal oxide CuxZnyO, which is prepared by a coprecipitation method by varying the molar ratio of Cu and Zn in the catalytic system. The prepared mixed metal oxide CuxZnyO was evaluated for catalytic performance for toluene oxidation. Various parameters of the catalytic evaluation were studied in order to ascertain the optimum condition for the best catalytic performance. The results indicate that aging time, calcination temperature, reaction temperature, and feed rate influence catalytic performance. It was found that the catalyst interfaces apparently enhanced catalytic activity for toluene oxidation. The XRD diffractograms reveal the crystalline nature of the mixed metal oxide formed and also confirm the coexistence of hexagonal and monoclinic crystalline phases. The catalyst prepared by aging for 4 h and calcined at 450 °C was found to be the best for the conversion of toluene to benzaldehyde while the reactor temperature was maintained at 250 °C with toluene fed into the reactor at 0.01 mL/min. The catalyst was active for about 13 h.

NiFe2O4 nanoparticles: an efficient and reusable catalyst for the selective oxidation of benzyl alcohol to benzaldehyde under mild conditions

Benzaldehyde is one of the most important and versatile organic chemicals for industrial applications. This study explores a milder approach for the fabrication of NiFe₂O₄ nanoparticles (NPs) for use as a catalyst in the selective oxidation of benzyl alcohol to benzaldehyde. A co-precipitation method coupled with hydrothermal aging has been adopted to synthesize NiFe₂O₄ NPs in the absence of any additive. Different techniques such as electron microscopy, diffractometry, and photoelectron spectroscopy have been used to characterize the products. The results showed that the synthesized NiFe₂O₄ NPs are spherical, pure, and highly crystalline with sizes below 12 nm possessing superparamagnetic behaviour. The catalytic activity of the synthesized NiFe₂O₄ NPs has been assessed in the selective oxidation of benzyl alcohol under ambient reaction conditions. A conversion of 85% benzyl alcohol with 100% selectivity has been attained with t-butyl hydroperoxide at 60 °C in 3 h. With the optimized reaction conditions, the generality of the newly developed protocol has been expanded to a wide array of substituted benzyl alcohols with good performance. The NiFe₂O₄ nanocatalysts are magnetically separable and are reusable up to five cycles without loss of catalytic activity.

Facile Sonochemical Preparation of Au-ZrO2 Nanocatalyst for the Catalytic Reduction of 4-Nitrophenol

High-intensity ultrasonic waves have great potential for the green synthesis of various nanomaterials under mild conditions and offer an excellent alternative for hazardous chemical methods. Herein a facile approach for the eco-friendly synthesis of Au-ZrO2 nanocatalyst with a high catalytic activity using a facile ultrasonic method is presented. Gold (Au) in the nanosize regime was successfully deposited on the surface of solvothermally synthesized monodispersed ZrO2 nanoparticles (ZrO2 NPs) in a very short period of time (5 min) at room temperature. Spherical shape small size Au nanoparticles that are uniformly dispersed on the surface of ZrO2 nanoparticles were obtained. Notably, in the absence of ZrO2 nanoparticles, HAuCl4 could not be reduced, indicating that nano-sized ZrO2 not only acted as support but also helped to reduce the gold precursor at the surface. The as-prepared Au-ZrO2 nanocatalyst was characterized by various techniques. The Au-ZrO2 nanocatalyst served as a highly efficient reducing catalyst for the reduction of 4-nitrophenol. The reaction time decreased with increasing the amount of catalyst.