Pt Catalyst Supported On Nitrided Carbon For Hydrogenation Of Cinnamaldehyde

Selective hydrogenation of a, β-unsaturated aldehydes is one of the key reactions in chemical industry, producing important raw materials and intermediates for flavors, fragrances, cosmetics, pharmaceuticals and bactericides, etc. Due to the reactivity difference between conjugated C=O and C=C bonds, a series of competitive reactions could happen during hydrogenation, resulting in diverse products. It is therefore of profound significance to investigate the design/fabrication of new hydrogenation catalytsts with better activity and selectivity for precise control of reaction and continuous improvement of industrial profit.As a new type or modification of carbon material, nitrided carbon has triggered enormous interest. The composition, structure and property of carbon can be tailored or altered by the incorporation of nitrogen, thus being promising to tune the performance of the supported hydrogenation catalyst. Furthermore, integration of magnetic component with nitrided carbon could offer a practical solution for efficient separation and recycling of the supported catalyst in selective hydrogenation.In the thesis work, two types of catalysts, Pt/Fe3O4@C-N and Pt/g-C3N4 were prepared, using platinum as catalytically active component and magnetic or nonmagnetic nitrided carbon material as carrier. The catalysts were evaluated in selective hydrogenation of cinnamaldehyde to explore the relationship of composition, structure and performance:1. Magnetic nanospheres of Fe3O4 were solvothermally prepared, and then hydrothermally coated with N-doped carbon material to develop magnetic core-shell structured carrier Fe3O4@C-N. Finally Pt was loaded in-situ onto Fe3O4@C-N by refluxing chloroplatinic acid precursor in reductive ethylene glycol to achieve the target catalyst Pt/Fe3O4@C-N, which was subjected to characterization by elemental analysis, Fourier transform infrared spectroscopy (FT-1R), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X ray photoelectron spectroscopy (XPS) and X ray diffraction (XRD). The results indicates that themagnetic Fe3O4 nanospheres are monodispersed and narrow-sized, with N-doped carbon layer (around 10 nm thick) well coated on their surface, and Pt nanoparticles (2-3 nm in diameter) uniformLy dispersed on N-doped carbon layer without significant agglomeration.2. The catalyst Pt/Fe3O4@C-N was evaluated using selective hydrogenation of cinnamaldehyde. Typically, the effect of nitrogen content in N-doped carbon on hydrogenation was investigated. The influence of reaction temperature, hydrogen pressure and loading percentage of Pt on hydrogenation, as well as the reusability of the catalyst was also explored. Compared to Pt nanocatalysts loaded on undoped carbon (65% conversion of cinnamaldehyde,93.2% selectivity for cinnamyl alcohol), those supported by N-doped carbon exhibit significantly improved catalytic performance, resulting in 82.6% conversion of cinnamaldehyde and 98% selectivity for cinnamyl alcohol when the nitrogen content reaches 2.9%. Under the external magnetic field, the catalyst can be quickly separated from the reaction system, and thecatalytic performance remains unchanged after being recycled for 5 times.3. Layered carbon nitride g-C3N4 was prepared through high temperature calcination of urea, and Pt nanoparticles were loaded onto g-C3N4via in-situ reduction by ethylene glycol to fabricate Pt/g-C3N4 catalysts, which were characterized by FT-IR, TEM, SEM, XPS and XRD analyses. The effect of g-C3N4 support obtained under different calcination temperatures on selective hydrogenation of cinnamaldehyde was studied.The results indicate that the g-C3N4 support incorporates a large amount of N-containing groups which help to stabilize 2-3 nm Pt nanoparticles uniformLy dispersed on g-C3N4 surface. The calcination temperature for g-C3N4 preparation had a significant effect on the performance of the catalyst for selective hydrogenation. Pt supported on g-C3N4 being calcinated at 550℃ exhibited an appreciable activity,30% conversion of cinnamic aldehyde and 66% selectivity for cinnamic alcohol under relatively mild condition. No obvious deterioration of the activity is observed after three times of usage. However, both activity and recyclability need further improvement as compared to Pt/Fe3O4@C-N.