The Preparation Of Pt Nanocrystal/Hydrotalcite Catalysts And Their Performance Research In Hydrogenation Of α,β-Unsaturated Aldehyde

Cinnamaldehyde(CMA), a typical α,β-unsaturated aldehyde, is one of important chemical raw materials. The unsaturated alcohols obtained by selective hydrogenation of C=O bonds have a wide range of application, which are usually the important intermediates used in the production of fragrances, pharmaceuticals and cosmetics. However, compared with the hydrogenation of C=O bond, the addition of hydrogen to the conjugated C=C bond is thermodynamically favored. The fabrication of catalysts with high activity and high selectivity for C=O bond has attracted extensive interesting of the researchers.The hydrotalcite, also known as layered double hydroxide(LDH), is a kind of anionic layered clay materials. Because of the versatility, low price as well as the characteristic of tunable compositions and exchangeable anions, the material has been comprehensively used as the catalytic materials. In this work, the Platinum nanocatalysts(Pt NCs) supported on LDH were synthesized by reducing the Pt Cl62- in solution and interlayer of LDH, respectively, through a simple hydrothermal reaction with alcohol as the reductant. Choosing the cinnamaldehyde(CMA) hydrogenation reaction to research the catalytic performance of prepared catalysts. The detail contents were as follows:(1) The fabrication and characterization of CO32--LDH / NO3--LDHThe CO32- ions intercalated hydrotalcite(CO32--LDH) was prepared through a similar separated nucleation/aging method by using the mixed salt solution of Mg(NO3)2·6H2O and Al(NO3)3·9H2O as well as the mixed alkali solution of Na OH and Na CO3. Similarly, the NO3--LDH was prepared by using the same method with Na OH as the alkali solution. Transmission electron microscopy, X-Ray powder diffraction and Fourier-transform infrared spectroscopy analysis have been employed to characterize the prepared LDH. The results showed that lamellar LDHs with different anions intercalated, smaller particle size(30-40 nm) and uniform size distribution were synthesized through the similar separated nucleation/aging method. And the prepared LDHs were used to support the Pt nanocatalysts in the following studies.(2) The fabrication of Pt nanocatalysts supported on CO32--LDH and the performance research of cinnamaldehyde hydrogenationPt nanocatalysts supported on CO32--LDH were synthesized in an alcohol(ethylene glycol, ethanol, methanol) /tetradecyl trimethyl ammonium bromide(TTAB) system through a one pot hydrothermal reaction. X-Ray powder diffraction, Fourier-transform infrared spectroscopy, Transmission electron microscopy and X-ray photoelectron spectroscopy techniques were used to characterized the catalysts. The catalytic performances of the supported Pt nanocatalysts were studied in the selective hydrogenation of cinnamaldehyde. Furthermore, the effects of different reductants, reaction time and reaction temperature on catalytic performance were explored. The results indicated that the catalyst reduced by ethylene glycol(Pt/LDH-EG) had the highest activity(TOF=2.314 s-1) and comparative highly C=O selectivity(78.8%) under mild reaction conditions. In addition, the stability of Pt/DLH-EG catalyst is favourable. The conversation could still remain above 85%, and the selectivity of C=O bonds is 72.2% after recycling four times.(3) The in situ fabrication of supported Pt nanocatalysts using NO3--LDH as the precursor and the performance research of cinnamaldehyde hydrogenationThe in situ fabrication of LDH supported Pt nanocatalyst(Pt-s/LDH-EG) was achieved by ion-exchange reaction(Pt Cl62- substituted for NO3-) and subsequently the EG/TTAB reduction reaction and in situ growth of Pt NCs on the LDH sheet. The characterization techniques of X-Ray powder diffraction, Fourier-transform infrared spectroscopy, Transmission electron microscopy and X-ray photoelectron spectroscopy were used to explore the catalyst. The selective hydrogenation reaction of cinnamaldehyde was employed to research the activity, selectivity and stability of the catalyst. Meanwhile, the effects of reaction time, reaction temperature and solvents on catalytic performance were discussed. It has the conclusion that the catalyst has comparative highly CMA conversation(92.6%), C=O selectivity(75.5%) and good stability in ethanol solvent. After four times recycling, the conversation could remain above 83% and the C=O selectivity was almost unchanged, which was bout 72.3%.In conclusion, here we used the versatility LDH as the support to prepare the supported Pt nanocatalysts through a hydrothermal reaction in EG-TTAB system. The prepared catalysts were chemically probed in the selective hydrogenation of cinnamaldehyde and high activity, C=O selectivity and favourable reusability were achieved. It supplied an important reference value for catalysts designing and practical application in selective hydrogenation of α, β-unsaturated aldehyde.