Abstract
The role of ZrO2 as different components in Ni-based catalysts for CO2 reforming of methane (CRM) has been investigated. The 10 wt.% Ni supported catalysts were prepared with ZrO2 as a support using a co-impregnation method. As a promoter (1 wt.% ZrO2) and a coactive component (10 wt.% ZrO2), the catalysts with ZrO2 were synthesized using a co-impregnation method. To evaluate the effect of the interaction, the Ni catalyst with ZrO2 as a coactive component was prepared by a sequential impregnation method. The results revealed that the activity, the selectivity, and the anti-coking ability of the catalyst depend upon the ZrO2 content, the Ni-ZrO2 interaction, basicity, and oxygen mobility of each catalyst resulting in different Ni dispersion and oxygen transfer pathway from ZrO2 to Ni. According to the characterization and catalytic activation results, the Ni catalyst with low ZrO2 content (as a promoter) presented highest selectivity toward CO owning to the high number of weak and moderate basic sites that enhance the CO2 activation-dissociation. The lowest activity (CH4 conversion ≈ 40% and CO2 conversion ≈ 39%) with the relatively high quantity of total coke formation (the weight loss of the spent catalyst in TGA curve ≈ 22%) of the Ni catalyst with ZrO2 as a support is ascribed to the lowest Ni dispersion due to the poor Ni-ZrO2 interaction and less oxygen transfer from ZrO2 to the deposited carbon on the Ni surface. The effect of a poor Ni-ZrO2 interaction on the catalytic activity was deducted by decreasing ZrO2 content to 10 wt.% (as a coactive component) and 1 wt.% (as a promoter). Although Ni catalysts with 1 wt.% and 10 wt.% ZrO2 provided similar oxygen mobility, the lack of oxygen transfer to coke during CRM process on the Ni surface was still indicated by the growth of carbon filament when the catalyst was prepared by co-impregnation method. When the catalyst was prepared by a sequential impregnation, the intimate interaction of Ni and ZrO2 for oxygen transfer was successfully developed through a ZrO2-Al2O3 composite. The interaction in this catalyst enhanced the catalytic activity (CH4 conversion ≈ 54% and CO2 conversion ≈ 50%) and the oxygen transport for carbon oxidation (the weight loss of the spent catalyst in TGA curve ≈ 7%) for CRM process. The Ni supported catalysts with ZrO2 as a promoter prepared by co-impregnation and with ZrO2 as a coactive component prepared by a sequential impregnation were tested in combined steam and CO2 reforming of methane (CSCRM). The results revealed that the ZrO2 promoter provided a greater carbon resistance (coke = 1.213 mmol·g−1) with the subtraction of CH4 and CO2 activities (CH4 conversion ≈ 28% and CO2 conversion ≈ %) due to the loss of active sites to the H2O activation-dissociation. Thus, the H2O activation-dissociation was promoted more efficiently on the basic sites than on the vacancy sites in CSCRM.
Highlights
Among the different routes for CO2 utilization, CO2 reforming of methane (CRM) is regarded as one of the most beneficial reactions for energy and environment
The 10 wt.% Ni/Al2O3 catalyst with a 1 wt.% ZrO2 promoter was prepared by the co-impregnation method (10Ni-1Zr/Al2O3(CI))
The 10 wt.% Ni/Al2O3 catalysts with a 10 wt.% ZrO2 coactive component were prepared by the co-impregnation (10Ni-10Zr/Al2O3(CI)) and sequential impregnation methods (10Ni10Zr/Al2O3(SI)) in order to study the effect of the different interactions in the catalyst
Summary
Among the different routes for CO2 utilization, CO2 reforming of methane (CRM) is regarded as one of the most beneficial reactions for energy and environment. Certain studies reported the effect of ZrO2 as a different component, the role of them derived from their physicochemical properties that related to the CRM and CSCRM performances of Ni catalysts are required to be more clarified under the precisely similar condition These relations can fulfil the detail of catalyst design for methane reforming processes. 10 wt.% ZrO2 was loaded with 10 wt.% Ni onto the Al2O3 support using co-impregnation and the sequential impregnation method to generate the different interactions of Ni-ZrO2 on the prepared catalysts Physicochemical properties of these catalysts were comprehensively characterized by X-ray diffraction (XRD), N2 adsorption–desorption, the temperature-programmed desorption of hydrogen (H2-TPD), the temperature-programmed reduction of hydrogen (H2-TPR), the temperatureprogrammed desorption of carbon dioxide (CO2-TPD) and the temperature-programmed desorption of oxygen (O2-TPD).
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.