Spontaneous activation behavior of Ni3Sn, an intermetallic catalyst, for hydrogen production via methanol decomposition
Introduction
In recent years, hydrogen production from methanol has attracted much research attention, as methanol has many qualities that are desirable for this reaction, such as its low cost and high H/C molar ratio [1], [2]. Much effort has been made to develop an efficient, low-cost catalyst for hydrogen production from methanol. Ni-based catalysts have been widely studied for this reaction, and their catalytic performance has been significantly improved in the past 30 years [3], [4], [5]. However, a drawback of these catalysts is the formation of methane from the side reaction of the hydrogen and carbon monoxide, which decreases the efficiency of hydrogen production. Therefore, it is necessary to design Ni-based catalysts that suppress this methanation reaction.
In the previous studies, it has been reported that Ni–Sn alloy displays a high selectivity for the desired products as it suppresses the production of methane during the reaction [6], [7], [8], [9]. In the reports the formation of a Ni3Sn intermetallic compound (IMC) is believed to be responsible for the improved catalytic properties in Ni–Sn alloy catalysts. In our previous work, we investigated the catalytic properties of Ni3Sn and Ni3Sn2 IMCs in the production of hydrogen from methanol decomposition. It was found that the catalytic activity of Ni3Sn was significantly improved with increasing reaction time, i.e., Ni3Sn was spontaneously activated during methanol decomposition [10]. However, the reasons for this spontaneous activation remain unclear. Therefore, it is first of all necessary to investigate the fundamentals of this behavior, such as temperature dependence and surface microstructure changes, and then to discuss the mechanism of the activation.
In this study, we examined the temperature dependence of the catalytic properties of Ni3Sn for methanol decomposition. The microstructure and surface morphology changes of the catalyst during the reaction were investigated to better understand its potential activation mechanism.
Section snippets
Sample preparation
Ni3Sn ingots were prepared by melting a stoichiometric mixture of metallic nickel and tin in a high-frequency vacuum melting furnace. The ingots were crushed in air and filtered to obtain particles of <75 μm diameter.
Catalytic activity measurements
The isothermal tests described in our previous report [11] were used to measure the catalytic activity of the samples in a conventional fixed-bed flow reactor consisting of a quartz tube with an internal diameter of 8 mm. Each catalyst sample weighed 0.4 g. Prior to methanol
Catalytic activity
The isothermal tests of methanol decomposition were carried out at 713, 793, and 873 K. Fig. 1 shows the conversion of methanol over Ni3Sn powder plotted as a function of decomposition time. The initial methanol conversion measured after 3 min of starting introduction of methanol is 2.4% at 713 K, 6.1% at 793 K, and 17.8% at 873 K. With increasing time on stream, the conversion slightly increases to 3.1% after 45 h at 713 K. However, it significantly increases with increasing temperature, and
Conclusions
The catalytic properties and spontaneous activation behavior of the single-phase Ni3Sn catalyst were investigated for decomposing methanol at 713, 793, and 873 K, and the following results were obtained:
- 1.
Ni3Sn showed an increase in the catalytic activity for methanol decomposition with increasing reaction time at 713, 793, and 873 K. The spontaneous activation depended on the decomposition temperature. Higher catalytic activity was obtained at higher decomposition temperatures.
- 2.
Ni3Sn showed high
Acknowledgments
The synchrotron XPS experiments were performed using SUREAC 2000 in BL23SU at SPring-8 under the approval of the Japan Synchrotron Radiation Research Institute (JASRI) and the Japan Atomic Energy Agency (JAEA) (proposals no. 2011B3806, 2012A3806, 2013A3873, 2013B3873, and 2014B3873). This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant number 22560769.
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