Dry reforming of methane to test passivation stability of Ni/ Al2O3 catalysts

• Published in: Applied catalysis. A, General Vol. 612; p. 117987
• Main Authors: Franz, Robert, Tichelaar, Frans D., Uslamin, Evgeny A., Pidko, Evgeny A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 25.02.2021; Elsevier Science SA
• Subjects: Aluminum oxide; Catalyst deactivation; Catalysts; Catalytic activity; Dry reforming of methane; Heterogeneous catalysis; Impact analysis; Low temperature; Metal particles; Methane; Nickel; Overheating; Oxidation; Passivation; Passivity; Pretreatment; Reforming; Sintering; Temperature; Heterogeneous catalysis; Nickel; Catalyst deactivation; Dry reforming of methane; Passivation
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2021.117987

[Display omitted] •Conversion and coking in dry reforming used to track sintering of Ni/Al2O3 catalysts and compare Ni particle sizes.•Dry reforming enables tracking of Ni sintering with only 10 mg of sample. Catalyst passivation refers to the formation of a protective oxide layer on the active metal particles that prevents their oxidation when exposed to air. Common passivation procedures, when applied to Ni/ Al2O3 catalysts, typically result in a significant decrease of the overall Ni surface area and, accordingly, the catalytic activity. Nevertheless, passivation and reactivation is an attractive pre-treatment option for this system. Ni/ Al2O3 typically requires reduction temperatures much higher than the desired reaction temperature, whereas reactivation of passivated samples is a low-temperature reduction. This can be used to avoid temperature limitations of existing systems. Thus, more insight into the passivation process of this system is desirable. In this work we analyzed the impact of passivation on the catalytic performance of a series of Ni/ Al2O3 catalysts in dry reforming of methane. This approach allows for the elimination of scale effects during passivation. We show that changes in conversion and especially of the coke content can be used to track sintering of Ni particles. These metrics allows to identify an adverse effects of catalyst passivation in excess O2, which gives rise to rapid local overheating and, accordingly, Ni sintering even when operating at tens of mg catalyst scale. Our study demonstrates that such problems are not limited to scaling issues and sufficient care must be taken even on a lab-scale when passivating Ni/ Al2O3 catalysts.