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Dependence of carbon dioxide hydrogenation on the structure of zirconia-based rhodium catalyst
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Kemian tekniikan korkeakoulu |
Master's thesis
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CHEM3021
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en
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77+3
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Abstract
Catalytic CO2 conversion into value added products has been one of the major study due to high energy demand and increasing atmospheric CO2 concentration. A catalytic reaction itself fulfills the Principles of Green Chemistry, but finding a catalyst for CO2 conversion at optimal temperature and atmospheric has been a greatest challenge. Studies have shown the structure of the catalyst is vital in CO2 hydrogenation for the product selectivity and reaction conditions. Support plays an important role in a reaction; where ordered struc-ture, high surface area and active sites are of high concern for a promising catalyst. This thesis has been made to study the rely of CO2 hydrogenation on the structure of the cata-lyst.
Support monoclinic zirconia nanorods (ZrO2 NRs) were prepared via hydrothermal synthe-sis and Rhodium (0.5 and 2 wt%) was loaded via wet impregnation. Activity tests were con-ducted for carbon dioxide hydrogenation under atmospheric pressure and at 200 °C. The performance of the catalyst was compared with Rh loaded catalyst on commercial mono-clinic zirconia support (com ZrO2). During the experiment, the effect of parameters such as the Rhodium content and WHSV on the performance of the catalysts were compared.
200 mg of catalyst was tested in CO2 hydrogenation, which was carried out for 4 h with WHSV 1500 h-1 to 6000 h-1. Catalyst was diluted with SiC for the higher loading of Rhodium. Catalyst prepared 0.5 wt% Rh in com ZrO2 support resulted higher conversion and CH4 se-lectivity (C = 5.23 %, SCH4=64.9 %) than with ZrO2 NRs (C = 4.7 %, SCH4=36.9 %) . With 2 wt% Rh, CH4 selectivity increased for com ZrO2 supported catalyst (SCH4=75.7 %). From the sorp-tion experiments, the Rhodium particles were bigger in size on ZrO2 NRs than on com ZrO2 which could have resulted less conversion and CH4 selectivity. An interesting result, with the formation of small amounts of higher alkanes (ethane, propane) during hydrogenation, was observed. The conversion and selectivity of ZrO2 NRs supported catalyst could not result better than com ZrO2 supported catalyst. The capping agent, NaOL, was found to be occupying the active sites on the ZrO2 NRs support and thorough removal of it could result better conversion.
Nevertheless, the conversion and selectivity of zirconia-based Rhodium catalyst in CO2 hydrogenation at low temperature and atmospheric pressure could open up a promising objective for the future research.