Short CommunicationThe synergistic effect of the structural precursors of Cu/ZnO/Al2O3 catalysts for water–gas shift reaction
Graphical Abstract
Research Highlights
► The Cu/ZnO/Al2O3 catalysts (Cu/Zn=1, Al=4–24 mol%) were prepared by co-precipitation for low-temperature water–gas–shift reaction in H2-rich feed gas. ► The Cu/ZnO/Al2O3 catalysts were characterized by means of on-line gas chromatographs, XRD, DSC and TPR. ► The synergistic effect of the structural precursors was detected in catalyst containing Al level of 4–24 mol%. ► The aurichalcite has been partially intercalated into the hydrotalcite and assimilated the surrounding structure during precipitation.
Introduction
Almost 95% of the hydrogen supply is produced from the reforming of coal, natural gas, crude oil, biomass and organic wastes [1], but this reformed gas contains 1% to 10% CO, which could destruct the performance of the Pt electrode in fuel cell system. WGSR (CO + H2O → CO2 + H2) is often used to obtain hydrogen for fuel cells and other industrial applications [2]. The Cu/ZnO/Al2O3 catalysts with high efficiency and low cost have been widely applied in industries for WGSR [3], [4], [5].
For Cu/ZnO/Al2O3 catalysts, it is well known that the Cu particle size and nature of the oxide support affect the performance of the WGS catalyst [6], [7]. Much attention in previous work was focused on the structure characteristics of the calcined catalysts, such as the low-temperature reducibility [8], [9], [10], [11], the interaction between Cu and ZnO [12], [13], the Cu surface area [14], electronic defect and the copper microstrain [15], but few studies concerning the influence of structural interaction of the hydroxycarbonate precursors on the catalyst performance were reported. However, the influence has a critical impact on their structures and performances of the activated catalysts. The Cu/ZnO/Al2O3 catalysts are usually prepared by co-precipitation and consist of a mixture of aurichalcite, hydrotalcite or malachite after precipitation [8], [16], [17], [18]. And the phase distribution in the structural precursors is greatly impacted by the Al content [16]. Furthermore, the aurichalcite phase plays an important role in the catalytic activity when the hydrotalcite phase is attributed to the stability of catalysts for WGSR [8], [11]. But few researchers paid attention to the structural interaction among the structural precursors and their subsequent impact on the catalyst performance.
The objective of this study is to identify the synergistic effect of the structural precursors in Cu/ZnO/Al2O3 catalyst on the low temperature WGSR in simulated coke oven-derived syngas, and determine the potential forming mechanism by the characterization of their structures and physico-chemical properties using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and temperature programmed reduction (TPR).
Section snippets
Catalyst synthesis
Ternary Cu/ZnO/Al2O3 catalysts were synthesized by the co-precipitation method. The preparation procedure consisted of mixing aqueous metal nitrate solutions with ultrasonic treatment, adding the mixture of metal nitrate solution and Na2CO3 solution dropwise into a magnetic stirrer with de-ionized water at 333 K and pH 9, aging the resulting gel at 333 K for 24 h, filtering and washing the precipitate with de-ionized water, drying the cake in a vacuum oven at 383 K for 12 h, crushing the dried lump
Surface area and structural analysis of the catalysts
The nominal composition and specific surface area of the Cu/ZnO/Al2O3 catalysts with different Al contents are summarized in Table 1, from which it can be found that both the surface areas of structural precursors and mixed oxides approximately declined from 85 m2/g to 63 m2/g with the increasing Al content from 4% to 18%, and subsequently increased to 70 m2/g at the Al content of 24%. In other words, the Al content greatly impacted the surface area of the catalysts, which might be attributed to
Conclusion
Cu/ZnO/Al2O3 catalysts (Cu/Zn=1 and Al=4–24 mol %) were prepared by the co-precipitation and characterized by XRD, DSC and TPR. The results, with their WGS activities in the H2-rich feed gas, showed that the increasing content Al generally led to the increase of hydrotalcite, the decrease of aurichalcite, the decreasing interlayer distance of hydrotalcite and the gradually enhanced thermal stability of hydrotalcite. But in Cu–Zn–Al 3, hydrotalcite was replaced by aurichalcite, its interlayer
Acknowledgement
The authors gratefully acknowledge the financial support from the National High Technology Research and Development Program of China (2006AA11A189), Science and Technology Commission of Shanghai Municipality (06DZ12212) and National Engineering Research Center of Advanced Steel Technology (050209).
References (22)
Catal. Today
(2005)- et al.
J. Power Sources
(2005) - et al.
Appl. Catal A-Gen.
(1995) - et al.
J. Catal.
(2003) - et al.
Appl. Catal A-Gen.
(2008) - et al.
Appl. Catal A-Gen.
(1996) - et al.
J. Mol. Catal. A: Chem.
(2007) - et al.
Appl. Clay Sci.
(2009) Appl. Surf. Sci.
(1984)- et al.
Appl. Catal A-Gen.
(1995)
Appl. Catal A-Gen.
Cited by (31)
Water gas shift and sorption-enhanced water gas shift reactions using hydrothermally synthesized novel Cu–Mg–Al hydrotalcite-based catalysts for hydrogen production
2021, Renewable and Sustainable Energy ReviewsSurface structure–activity relationships of Cu/ZnGaO<inf>X</inf> catalysts in low temperature water–gas shift (WGS) reaction for production of hydrogen fuel
2020, Arabian Journal of ChemistryCitation Excerpt :The highest CO conversion (72% at 200 °C) of Cu-Ce-Zn (Tabakova et al., 2007) catalyst prepared by urea-nitrate combustion method was achieved with an increase in surface area and a decrease of Ce particle size and a high WGS rate was achieved by Cu-ZnO/CeAl catalyst prepared by the wet impregnation method. Co-precipitated Cu-Zn-Al-3 (Cu/Zn/Al = 44/44/12) in the study (Fu et al., 2011) of Cu/ZnO/Al2O3 catalysts (Cu/Zn = 1 and Al = 4–24 mol %) with different content of Al, showed the highest CO conversion (95%) with a WGS rate of 15.8 × 10−4 s−1at temperature 200 °C. High activity was attributed to the structure of the catalyst for which was suggested partially intercalation of aurichalcite into the hydrotalcite and enhanced the interaction among the supports and active centers of the catalyst.
Highly efficient copper-manganese oxide catalysts with abundant surface vacancies for low-temperature water-gas shift reaction
2020, International Journal of Hydrogen EnergyAn important parameter for synthesis of Al<inf>2</inf>O<inf>3</inf> supported Cu-Zn catalysts in low-temperature water-gas shift reaction under practical reaction condition
2019, International Journal of Hydrogen EnergyThe alcohol-modified CuZnAl hydroxycarbonate synthesis as a convenient preparation route of high activity Cu/ZnO/Al <inf>2</inf> O <inf>3</inf> catalysts for WGS
2019, International Journal of Hydrogen Energy