Studies On Selective Catalytic Oxidation Of P-Cresol To P-Hydroxybenzaldehyde

Selective oxidation is one of the privileged ways in transformation of hydrocarbons to more valuable and more useful product, such as alcohol, aldehyde, acid and other oxygenates. And it is also one of the important ways to exploit hydrocarbon. But product of selective oxidation is not favored in thermodynamics, compared to deep oxidation product CO₂ and H₂O. It is well-known, therefore, selective oxidation of hydrocarbons is a challenge way in chemical research.This paper summarized development of selective oxidation of hydrocarbons, especially about oxidation of p-cresol to p-hydroxybenzaldehyde. The main aim of this paper was research of heterogeneously catalyzed selective oxidation ofp-cresol to p-hydroxybenzaldehyde with molecular oxygen in liquid phase. It was found that cobalt and magnesium oxides catalyst supported on carrier had excellent activity in oxidation ofp-cresol.The CoMg/γ-Al₂O₃ catalyst was prepared by cheap metal cobalt salt as active component, magnesium salt as promoter, and γ-Al₂O₃ as carrier using the stepwise impregnation method. The performances of these catalysts were characterized using XRD, TG-DTA, TPR methods. The optimum conditions of catalyst preparation were achieved according to the results of catalyst characterization and oxidation ofp-cresol, the effect of preparation condition on catalytic performance was analyzed at the same time. Results show that the calcined temperature, time and concentration of solution have great influence on catalytic performance. The catalyst includes CO3O4 and Mg_xCo_1-xoxides (x= 0.22,0.23,0.18), and this two oxides have the similar structures. CO3O4 is active phase of the catalyst, and Mg_xCo^1-xoxides are favored in the oxidation ofp-cresol to p-hydroxybenzaldehyde. At the same time, it is possible that absorbed oxygen is the active oxygen in selective gas-phase oxidation of p-cresol and there are two kinds of active sites on the surface of the catalyst.Under the optimum condition of catalyst preparation, the condition of oxidation reaction was optimized. The best result is when the conversion of p-cresol reaches98.47%, the selectivity for /?-hydroxybenzaldehyde is 99.13% under the mild condition, and this result exceeds others reported by literatures.