Study Of Supporting Nanocarbon Materials Catalyst For The Phenylacetylene Hydrogenation Reaction

Styrene is an important basic organic chemical raw material. However, styrene feedstock generally contains small amounts of phenylacetylene, which can not only affect the styrene production process but also make the performance of styrene polymerization products degradation. Therefore, the selective hydrogenation of phenylacetylene to styrene is of great importance in the pyrolysis gasoline method to recycle styrene and the polymer production with styrene as monmer and other industrial applications. The phenylacetylene selective hydrogenation catalysts are mainly palladium(Pd) and nickel(Ni) based catalysts. This paper chosed three different graphitization degrees of carbon nanotubes as the carriers and synthesized the supported catalysts of Pd and Ni base with different methods respectively, which were characterized by scanning electron microscope(SEM) and transmission electron microscope(TEM) to study the morphology and structure of the catalysts. The prepared catalysts were used for the phenylacetylene hydrogenation reaction in atmospheric glass reactor and continuous flow hydrogenation system of H-Cube Pro respectively and recycled after the reaction. The catalysts were characterized by using inductively coupled plasma optical emission spectroscopy(ICP-OES), X-ray diffraction(XRD), Raman spectroscopy(Raman), and X-ray photoelectron spectroscopy(XPS) before and after the reaction. In addition, the effect of various factors on the catalytic performance under the continuous flow condition was studied. The main work of the paper was as follows:1. The main catalyst supports investigated in this paper, were three different kinds of carbon nanotubes, PSCNTs, LHTCNTs and HHTCNTs, which were in the same family of carbon nanotubes. The tubular structure and different morphology on the surface of three kinds of carbon nanotubes were observed by SEM and TEM. The different degree of graphitization of three kinds of carbon nanotubes could be seen by XRD and Raman analysis. The PSCNTs was with the largest defect degree, the highest disorder and the lowest degree of graphitization, the HHTCNTs with the minimized defect degree, the minimum disorder and the highest degree of graphitization, while the LHTCNTs with the centered graphitization degree. Nitric acid treatment was carried out on the carbon nanotubes and there were a series of characterization for the carbon nanotubes after acid treatment. The analysis by SEM, TEM, XRD, Raman, and XPS showed that acid treatment could remove the amorphous carbon in the carbon nanotubes effectively to purify the carbon nanotubes, and import oxygen-containing functional groups on the surface of carbon nanotubes, such as hydroxyl, carboxyl and carbonyl. The graphitization degree of three carbon nanotubes after acid treatment was still in the order: the graphitization degree of the HHTCNTs was in turn higher than that of the LHTCNTs and PSCNTs.2. The single metal catalysts Pd/CNTs and Au/CNTs and the bimetallic catalyst Pd-Au/CNTs were prepared through the simple H2 reduction method at room temperature with the PSCNTs as the support. The catalytic performance for phenylacetylene selective hydrogenation of three catalysts was investigated in the atmospheric glass reactor, in which bimetallic Pd-Au/CNTs catalyst showed better catalytic performance than two single metal catalysts Pd/CNTs and Au/CNTs in the process of phenylacetylene selective hydrogenation to styrene. Through the ICP analysis Au nanoparticles in the Au/CNTs catalyst could hardly load on the functionalization carbon nanotubes because of the poor interaction between the Au nanoparticles and the CNTs support. The equally distributed metal nanoparticles with different size were observed on the carbon nanotubes surface by SEM and TEM. The characterization of catalysts through XRD, Raman, HRTEM/EDS and XPS showed that the Au particles in the bimetallic Pd-Au/CNTs catalyst could load on the carbon nanotubes owing to the tracking effect of Pd particles, the double metal forming the similar Au@Pd core-shell structure, most of the metal Pd particles being wrapped inside by Au shell, a small amount of Pd nanoparticles spreading on the surface of Au shell being the main active component of bimetallic catalyst. In addition, the analysis from XPS figures showed that there were electron transfer and interaction between two metal particles in the bimetallic catalyst.3. The 4 wt% catalysts Ni/PSCNTs, Ni/LHTCNTs and Ni/HHTCNTs were synthesized by the traditional impregnation method with three different graphitization degree carbon nanotubes PSCNTs, LHTCNTs and HHTCNTs as the supports. The morphology structure of catalysts was observed by SEM and TEM. The catalytic performance of three catalysts for phenylacetylene hydrogenation was investigated in continuous flow hydrogenation reactor H-Cube Pro, and the catalytic performance was in the order: Ni/PSCNTs > Ni/LHTCNTs > Ni/HHTCNTs. The three catalysts were also treated before the reaction under severe conditions and great changes of catalytic performance had taken place for the pretreated catalysts. The performance order was completely opposite: Ni/PSCNTs < Ni/LHTCNTs < Ni/HHTCNTs. The comparative analysis of XRD, Raman, and XPS for the catalysts before and after reactions showed that pretreatment had changed the nanostructure of Ni/CNTs catalysts. Through the comprehensive analysis of catalytic performance and nanomaterials structure, the catalytic mechanism of phenylacetylene hydrogenation reaction was discussed.4. In view of the advantages that the continuous flow hydrogenation system H-Cube Pro could evaluate and screen catalysts efficiently and be easy to change the parameters. The effects of main influencing factors(temperature, pressure, the amount of hydrogen and flow rate) on the catalyst Ni/PSCNTs for the phenylacetylene selective hydrogenation catalytic reaction were investigated with the H-Cube Pro as a test platform. The experimental results showed that various factors under continuous flow condition had different influences on catalytic performance in the phenylacetylene hydrogenation reaction. The reaction temperature should not be too high, and the optimized temperature was 20 ℃. The reaction pressure had a significant effect on phenylacetylene hydrogenation, and the target product styrene achieved a better yield under a slightly positive pressure conditions. The appropriate amount of hydrogenation was 24 m L/min. The product yield increased with the increasement of flow rate and the reaction flow rate should not be too low.