| α,β-unsaturated aldehyde is an important chemical raw materials for synthesis of saturated aldehydes, unsaturated alcohols, unsaturated alcohols and alkanes. Selective hydrogenation of the C=O double inα,β-unsaturated aldehyde could produce unsaturated alcohol, which is widely applied in spices, medicine, and other fine chemical products. In this work, a series of Pt-based catalysts were prepared and tested for gas phase selective hydrogenation of crotonaldehyde. The catalysts were characterized using X-ray powder diffraction analysis (XRD), X-ray fluorescence diffuse reflectance (XRF), inductively coupled plasma-atomic emission device element analysis (ICP-AES), CO chemisorption characterization, NH3 temperature-programmed (NH3-TPD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) techniques. it was found that the Pt/NaCl/ZrO2 catalysts were highly active in this reaction, and the active sites and mechanism of the reaction was discussed. The detailed results are as follows:1. Effects of NaCl on Pt/ZrO2 catalysts for selective hydrogenation of crotonaldehydeA series of NaCl-modified Pt/ZrO2 catalysts were prepared and tested for vapor phase selective hydrogenation of crotonaldehyde. It was found that the reactivities of the catalysts increased with NaCl contents, with the highest selectivity to crotyl alcohol (60.%) at a NaCl content of 1%. NH3-TPD and FTIR spectra of pyridine adsorption results indicated that the strength of surface Lewis acid of the catalysts was weakened with increasing NaCl contents, which was responsible for the enhancement of the reactivity. Diffuse reflectance infrared transform spectra of CO adsorption and X-ray photoelectron spectrometer results suggested that increased electron density on Pt species with the NaCl modification was responsible for the enhanced selectivity. However, high NaCl content (>3%) in the catalyst resulted in the growth of Pt particles and less interfacial Pt sites contacting with the surface Lewis acid sites, which was unfavorable for the selectivity.2. The effect of NaOH in the Pt/ZrO2 of crotonaldehyde hydrogenationBy using the chlorine-free chlorine ZrO2 and ZrO2 (Cl) as supports, the effect of alkali metal ion (Na+) on the catalytic performance was studied. It was found that the presence of Cl species strengthened the Lewis acidity, while the presence of Na+ changeed the electronic property of the Pt species. The results indicated that the addition of NaOH in the Cl-containing catalyst greatly enhanced the activity and selectivity to crotyl alcohol, while the addition of NaOH in the Cl-free catalyst suppressed the reactivity.3. The deactivation mechanism of the Pt/NaCl/ZrO2 and Pt/CeO2 catalysts.Pt/CeO2 and Pt/NaCl(1)/ZrO2 catalysts were prepared using deposition-precipitation and impregnation methods and tested for selective hydrogenation of crotonaldehyde. It was found that for the Pt/CeO2 catalyst, the conversion and the selectivity to crotyl alcohol decreased with time on stream. For the Pt/NaCl(1)/ZrO2 catalyst, the conversion decreased and the selectivity to crotyl alcohol kept constant with time on stream. The deactivation on the Pt/CeO2 catalyst was caused by the oxidation of the Ce3+ to Ce4+ during the reaction, accompanied by the deposition of carbon on the surface of catalyst. However, carbon deposition hardly adsorbed on the Pt/NaCl(1)/ZrO2 catalyst, which may be the reason that the selectivity to crotyl alcohol remained unchanged. |
