Nickel Supported Modified Ceria Zirconia Lanthanum/ Praseodymium/Yttrium Oxides Catalysts for Syngas Production through Dry Methane Reforming

Abstract:

Dry methane reforming (DRM) has recently received considerable attention as a perspective CO₂ utilization technology allowing the valorization natural gas and biogas. The commercialization of the DRM process depends on the use of more stable and active catalysts. The nickel-based catalysts are commonly used in the DRM reaction as they are effective in hydrogen production and nickel is a less expensive material compared to noble metals. However, Ni-based catalysts undergo fast deactivation. The stability of nickel catalysts in DRM reaction may be enhanced by introduction of supports or promoters with basic and/or redox properties. Thus, in this work, Ceria-Zirconia supports were modified by rare earth metals such as Lanthanum, Praseodymium and Yttrium in order to stabilize the raw materials and to promote the catalytic activity. Nickel was then impregnated on such supports and the modified catalysts were tested in dry methane reforming for syngas production since it was already reported that a promotion with nickel and yttrium lead to better activity in DRM catalytic tests over mesoporous materials. All promoted catalysts were characterized by the means of S_BET, XRD, TEM, H₂-TPR, CO₂-TPD in order to define the physical, textural and chemical properties. The influence of basicity on the catalytic activity was clearly evidenced. Moreover, the influence of Nickel loading was also studied. It was evidenced that an optimal Ni loading is needed in order to reach higher activity and stability in DRM.

• Periodical: Materials Science Forum (Volume 941)
• Pages: 2214-2219
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.941.2214
• Online since: December 2018
• Authors: Hong Rui Liu, Katarzyna Świrk, Maria Elena Galvez, Patrick da Costa*
• Keywords: Ceria-Zirconia Supports, Lanthanum, Nickel, Promotion, Syngas, Yttrium

References

[3] 2 Physico-chemical characterization Fig. 2 shows XRD patterns of reduced and spent catalysts. The Ni° crystallite size was calculated (based on reflection of metallic nickel at ca. 2θ = 44.5°) and presented in Table 2. Fig. 2B shows the reflection at ca. 26.7°, which is ascribed to graphitic carbon. The intensities of the carbon reflections are consistent with calculated carbon depostion (Table 2). A) B) Fig 2. XRD patterns of A) reduced catalysts, B) spent catalysts. The 15%Ni/Ce-Zr-La catalyst, which exhibited the best activity at low temperature range, presented the lowest Ni° crystallite size. Moreover, no sintering of the nickel was observed for this material, since the Ni° crystallite size did not change after reaction, i.e. 33.9 nm after run vs. 34.2 nm. On the contrary, for both Y and Pr-promoted catalysts, the size of the nickel decreased after run. This observation has been already reported in the literature on different support, such as Al2O3 and SiO2 supported catalysts [[] T. Nakayama, M. Arai, Y. Nishiyama, Dispersion of nickel particles supported on alumina and silica in oxygen and hydrogen, J. Catal. 87 (1984) 108-115. ], and can be attributed to a re-dispersion of the Ni particles during the DRM reaction. Fig. 3A presents H2-TPR profiles of reduced catalysts. A comparable consumption of hydrogen may be observed (ca. 1.7 mmol H2/gcatalyst), indicating that similar content of nickel is reduced for each sample. In H2-TPR profiles, three reduction peaks with a shoulder at about 315°C, 380°C and 560°C have been observed. The peaks below 400°C correspond to reduction of free NiOx species, the shoulder at 450°C can be ascribed to strong interaction in NiOx-support and reduction of ceria that mainly contribute to the last peak at 560°C [[] H.-S. Roh, H.S. Potdar, K.-W. Jun, J.-W. Kim, Y.-S. Oh, Carbon dioxide reforming of methane over Ni incorporated into Ce-ZrO2 catalysts, Applied Catalysis A: General, 276 (2004). 231-239. ]. Table 2. Ni crystallite size, H2 consumption, Total basicity and C deposition on studied catalysts. Catalyst Ni0 crystallite size [nm]* H2 Consumption from TPR.

[34] 2.

[33] 9.

[2] 00.

[55] 7.

[86] 9.

[82] 1.

[224] 7 569 15%Ni/Ce-Zr-Pr.

[40] 4.

[28] 1.

[1] 61.

[53] 7.

[71] 7.

[95] 9.

[221] 3 541 15%Ni/Ce-Zr-Y.

[59] 2.

[27] 3.

[1] 74.

[52] 8.

[79] 5.

[100] 2.

[232] 5 585 * calculated from XRD (sherrer equation REF), ** calculated from CO2 TPD plots, *** C Balance from DRM reaction at 750°C for 5h TOS Generally, the activity in DRM may be correlated with the basicity of the used catalysts [11]. Fig. 3B presents CO2 desorption profiles for reduced catalysts, where similar sholders and values of total basicity were observed (ca. 225 μmol CO2/g catalyst). Three CO2 desorption peaks were registered, at ca. 150°C, 375°C and 490°C corresponding to weak, medium and strong basic sites, respectively [10,11]. However, Y promotion led to the highest number of basic sites with strong strength, and the highest total basicity. A)B) Fig 3. A) H2 consumption from Temperature Programmed Reduction, B) CO2 desorption from Temperature Programmed Desorption of pre adsorbed CO2.

DOI: 10.1016/j.fuel.2019.116726

[4] Conclusion In this work, ceria-zirconia supports were modified by rare earth metals, such as lanthanum, praseodymium and yttrium in order to stabilize the raw materials and to promote the catalytic activity. The supports were impregnated with nickel nitrate, characterized by XRD, H2-TPR and CO2-TPD, and tested in dry methane reforming for syngas production. Similar catalytic activity was found in all tested catalysts, which may be ascribed to their similar basicity and Ni° crystallite size after catalytic run. However, at temperatures lower than 700°C, a change in H2/CO ratio was observed, since Y favours carbon forming reaction, whereas Pr and La lead to lower H2/CO ratio due to gasification of carbon deposit formed during the DRM process. The XRD analysis relieved similar Ni° crystallite size in all catalysts, and the re-dispersion of Ni particles in the spent samples was observed. As perspectives, in situ DRIFT experiments are in course in order to distinguish the different mechanisms occurring in DRM for all Y, La, Pr promoter. Reference.