Structure Sensitivity in Steam and Dry Methane Reforming over Nickel: Activity and Carbon Formation

Abstract

Hydrogen is currently mainly produced via steam reforming of methane (SMR: CH 4 + H 2 O → CO + 3H 2 ). An alternative to this process, utilizing carbon dioxide and thus potentially mitigating its environmentally harmful emissions, is dry methane reforming (DMR: CH 4 + CO 2 → 2CO + 2H 2 ). Both of these reactions are structure sensitive, that is, not all atoms in a catalytic metal nanoparticle have the same activity. Mapping this structure sensitivity and understanding its mechanistic workings provides ways to design better, more efficient, and more stable catalysts. Here, we study a range of SiO 2 -supported Ni nanoparticles with varying particle sizes (1.2−6.0 nm) by operando infrared spectroscopy to determine the active mechanism over Ni (carbide mechanism) and its kinetic dependence on Ni particle size. We establish that Ni particle sizes below 2.5 nm lead to a different structure sensitivity than is expected from and implied in literature. Because of the identification of CH x D x species with isotopically labeled experiments, we show that CH 4 activation is not the only rate-limiting step in SMR and DMR. The recombination of C and O or the activation of CO is likely also an important kinetically limiting factor in the production of synthesis gas in DMR, whereas for SMR the desorption of the formed CO becomes more kinetically limiting. Furthermore, we establish the Ni particle size dependence of carbon whisker formation. The optimal Ni particle size both in terms of activity for SMR and DMR, at 500 and 600 °C, and 5 bar, was found to be approximately 2−3 nm, whereas carbon whisker formation was found to maximally occur at approximately 4.5 nm for SMR and for DMR increased with increasing particle size. These results have direct practical applications for tuning of activity and selectivity of these reactions, while providing fundamental understanding of their working.

Butane Dry Reforming Catalyzed by Cobalt Oxide Supported on Ti2AlC MAX Phase

“…Dry reforming is a structure‐sensitive reaction, where the catalyst particle size affects its performance [43] . Thus, we compared the intrinsic activity of Co 3 O 4 /Ti 2 AlC and Co 3 O 4 /Al 2 O 3 catalysts based on their turnover frequency (TOF, Table 1).…”

Synthesis Chemistry and Properties of Ni Catalysts Fabricated on SiC@Al2O3 Core-Shell Microstructure for Methane Steam Reforming

“…The size of Ni NPs on the catalyst was large, which is unfavorable for both the catalytic activity and carbon formation. The MSR is structure sensitive, favoring small Ni particle sizes, while carbon formation is reported to increase with increasing particle size [27]. The precise control of Ni particle size and modulation of surface properties against sintering and coking is not covered in the scope of this work.…”

“…In this work, an attempt is not made to demonstrate the effects of enhanced heat and mass transport properties of the Ni/SiC@Al 2 O 3 catalysts in comparison to the conventional catalysts, which have been extensively researched in our previous work. In addition, MSR is reported to be structure sensitive [27], hence, a fine control of the dispersion and structure of Ni NPs also bears significant effects on the kinetics of the reactions. The aim of this work is to investigate the chemistry and synthesis methodology for production of Ni/SiC@Al 2 O 3 catalysts, and their stability and performance under the practical reaction conditions.…”

A Short Review on Ni Based Catalysts and Related Engineering Issues for Methane Steam Reforming

“…Calcium slowed down the carbon diffusion and the C-C formation rate, thus inhibiting the carbon deposition. Vogt et al studied the effect of the SiO 2 -supported nickel nanoparticle size, in the range 1.2-6.0 nm, on the methane steam reforming and dry methane reforming, by operando infrared spectroscopy, to determine the active mechanism and its kinetic dependence on the nickel particle size [69]. The results showed that very small supported Ni nanoparticles (<1.5 nm) were less active in the reforming processes, probably due to the quantum effects, which may play a rule for small nanoclusters.…”