Cyclic adsorption studies on carbon dioxide hydrogenation to methanol using diffuse reflectance infrared Fourier transform spectroscopy and mass spectrometry
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Journal Title
Journal ISSN
Volume Title
Kemian tekniikan korkeakoulu |
Master's thesis
Authors
Date
2021-06-15
Department
Major/Subject
Chemistry
Mcode
CHEM3023
Degree programme
Master's Programme in Chemical, Biochemical and Materials Engineering
Language
en
Pages
91+9
Series
Abstract
The transformation of carbon dioxide into useful product i.e., methanol using tailor-made catalysts is a crucial step towards reduction of carbon dioxide concentration in atmosphere. Studying the interaction between the gases (CO2 and H2) and the catalyst surface is of great significance as it helps to understand the reaction intermediates and pathways. As Cu and Zn metals, reportedly, are active towards CO2 hydrogenation to methanol, this work studied the cyclic adsorption of CO2 and H2 to understand the behaviour of Cu and Zn over zirconia samples towards adsorption of the fed gases. The formation of expected intermediate species i.e., carbonates, bicarbonates, formates, methoxy and methanol, over samples and the products formed were analysed using in-situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) and mass spectrometry (MS), respectively. The literature review discusses the concept of methanol economy and development of heterogeneous catalyst for CO2 to methanol conversion. Focus of study was given to the characterization of the catalytic materials used in CO2 to methanol reaction. The probe molecules i.e., CO2 and H2, and intermediate species and products, formed during the reaction were described in relation to the absorption bands displayed in DRIFTS. The experimental part of thesis initiated by obtaining the prepared zirconia-based samples i.e., ZrO2, Cu/ZrO2, Zn/ZrO2 and Cu/Zn/ZrO2, using incipient wetness impregnation for Cu impregnation and atomic layer deposition for Zn over zirconia. The cyclic adsorption tests consisted of three cycles of CO2 and H2 flow with Ar purge in between each gas flow at 450, 500 and 550 K, conditions that were defined after initial pre-study experiments. The results displayed that monodentate carbonates and bidentate bicarbonates were formed on all zirconia samples while formates were only observed with H2 flow in presence of Cu or Zn over zirconia. The formates had strong adsorption over the sample surface and seemed to form from monodentate carbonates. While bicarbonates were weakly adsorbed, these disappeared with inert gas purge and were not related to formate appearance. Among the samples, Zn/ZrO2 displayed promising results with a good ability to retain carbonates on the surface during CO2 flow and convert them to formates during H2 flow.Description
Supervisor
Puurunen, RiikkaThesis advisor
Arandia Gutierrez, AitorKeywords
cyclic adsorption, CO2 hydrogenation, methanol, in-situ DRIFTS, mass spectrometry