Preparation, Synthesis, and Physical and Catalytic Analysis of Nizno Catalysts for Selective Acetylene Hydrogenation
Open Access
- Author:
- Sim, Richard Sueyong
- Area of Honors:
- Chemical Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Robert Martin Rioux Jr., Thesis Supervisor
Dr. Michael John Janik, Thesis Honors Advisor - Keywords:
- acetylene
ethylene
catalyst
organo
synthesis
selective
hydrogenation
chemical
engineering
conversion - Abstract:
- Acetylene semi-hydrogenation reactions over Ni/ZnO catalysts of varying nickel weight loading (0.5, 1, 2, 5, and 10 wt %) were carried out in a batch reactor system. Catalysts were synthesized via wet impregnation technique and subsequently calcined, reduced, and characterized via x-ray diffraction (XRD). Catalysts were characterized after calcination and after reduction. The reduction of catalysts was performed via temperature programmed reduction (TPR), where the reduction temperature for Ni and was determined to be ~400oC; Ni reduction also facilitated reduction of Zn. XRD analysis of calcined samples confirmed the formation of NiO nanoparticles with minor Zn incorporation. Zn diffusion most likely occurs during calcination, which will require future investigation. After reduction of calcined samples, the samples were found to contain Ni4Zn, with higher weight loadings (5, 10 wt %) with more Ni than ZnO in their lattice structure, tending towards a solely Ni structure. The hydrogenation of acetylene over Ni/ZnO samples was monitored through regular sampling of the batch reactor gas effluent from gas chromatography-mass spectrometry (GC-MS), using isotopically-labeled acetylene as feed gas. The gas samples were run through a gas chromatograph paired with a mass spectrometer, from which catalytic data was determined. Further characterization continued on 2 wt % Ni/ZnO due to the low wt % of Ni, allowing more NiZn to form at Ni-ZnO particle contact areas, allowing ease of X-ray absorption near edge structure (XANES) analysis. After calcination, samples were reduced at various temperatures (400, 500, and 600oC). Despite a strong showing of selectivity, Ni/ZnO had an acetylene conversion to ethylene of ~18% at all reduction temperatures. Ni/SiO2, a control used for comparison to NiO without a chemically influencing support, was a more effective catalyst than Ni/ZnO. Although more ethane was produced from reaction, Ni/SiO2 had a higher conversion of acetylene to ethylene at ~40%. From Ni/ZnO GC-MS analysis, the carbon balance after reaction suggests a majority of the products as oligomers, more undesired than ethane. The goal of the catalyst is to remove as much acetylene as possible (a poison for polyethylene-production catalysts) to form ethylene. Ni/ZnO converts less acetylene to ethylene and creates more oligomers than any other product. However, Ni/SiO2, despite increased ethane production, produces ~40% ethylene and few oligomers. With proper separation, the ethane (single molecule) from Ni/SiO2 can more easily removed compared to oligomer separation (multiple molecules). Future work on the deactivation of reactive sites on Ni/ZnO particles may elucidate the phenomenon of ZnO shell formation on NiO; additionally, XRD analysis of calcined samples confirmed the formation of NiO nanoparticles with minor Zn incorporation. Zn diffusion may be occurring during calcination, which will require future investigation.