Vissanu Meeyoo

Autothermal reforming (ATR) is a viable option for reducing coke formation and energy consumption in hydrogen production processes. The space-resolved ATR of acetic acid as a model compound over the Ni/Ce_0.75Zr_0.25O₂ catalyst is performed using a spatial discretization approach by means of separating a reactor into up to 4 reaction zones. The spent catalysts from different zones were further characterized by ex situ XPS and TPO techniques to investigate the Ni oxidation states, coke morphology, and coke combustion. In addition, steam reforming (SR) and partial oxidation (POX) were similarly performed to decouple the effects of steam and oxygen from ATR. By comparing with SR, co-fed oxygen in ATR has significantly decreased the overall amount of coke formation with the implication on the reduced H₂ yield partially due to the CO oxidation. The co-fed oxygen consumed in the frontal section of the catalyst bed resulted in the oxidation of metallic Ni, decreasing the acetic acid conversion of the initial zone of its catalyst bed. Such oxidized Ni species could also be reduced by H₂ in the product stream of the previous zone resulting in a lower H₂ yield. Although oxygen can reduce the overall coke formation, its coke structures have been shifted from filamentous coke to the formation of polymeric, soft, and carbidic cokes. Those types of cokes seemed to be related to the formation of NiO that promotes acetate formation and decomposition. In sum, the presence of oxygen in the part of the catalyst bed results in the differences of the catalytic activity, the oxidation state of Ni, and the pattern of coke formation; this has created two recognizable reaction zones.

Ni-Ce-Zr-O_δ catalysts were prepared via one-pot hydrothermal synthesis. It was found that Ni can be partially incorporated into the Ce-Zr lattice, increasing surface oxygen species. The catalysts possess high surface areas even at high Ni loadings. The catalyst with Ni content of 71.5 wt.% is able to activate CO₂ methanation even at a low temperature (200 °C). Its CO₂ conversion and methane selectivity were reported at 80% and 100%, respectively. The catalyst was stable for 48 h during the course of CO₂ methanation at 300 °C. Catalysts with the addition of medium basic sites were found to have better catalytic activity for CO₂ methanation.

Thermochromic films based on vanadium dioxide (VO₂)/ethylene vinyl acetate copolymer (EVA) composite were developed. The monoclinic VO₂ particles was firstly prepared via hydrothermal and calcination processes. The effects of hydrothermal time and tungsten doping agent on crystal structure and morphology of the calcined metal oxides were reported. After that, 1 wt % of the prepared VO₂ powder was mixed with EVA compound, using two different mixing processes. It was found that mechanical properties of the EVA/VO₂ films prepared by the melt process were superior to those of which prepared by the solution process. On the other hand, percentage visible light transmittance of the solution casted EVA/VO₂ film was greater than that of the melt processed composite film. This was related to the different gel content of EVA rubber and state of dispersion and distribution of VO₂ within the polymer matrix phase. Thermochromic behaviors and heat reflectance of the EVA/VO₂ film were also verified. In overall, this study demonstrated that it was possible to develop a thermochromic film using the polymer composite approach. In this regard, the mixing condition was found to be one of the most important factors affecting morphology and thermo-mechanical properties of the films.