Abstract
Methane catalytic decomposition (MCD) over Ni/MCM-41 catalysts was tested in a microreactor to simultaneously produce hydrogen and carbon nanotubes (CNTs). The methane conversion reached 30% to 47% at a moderate temperature range from 400°C to 600°C and the catalytic activity of the catalysts remains stable during 500 min steam on time. CNTs were chiefly formed through tip-growth mode, due to the weak interaction between the metallic Ni and the support. Most of the Ni particles are located on the tip of the produced CNTs, which avoids rapid deactivation of the catalyst resulted from carbon encapsulation. Large Ni particles usually lead to the formation of CNTs with big diameter. During the reaction, the shape of Ni particles changed from pseudo-sphere to diamond-like. All the CNTs consist of multiple layer walls and are curved in certain degree.
Highlights
A great attention has been paid to the use of hydrogen on a very large scale in chemicals, food and petroleum refining industries, fuel cell technology, space exploration and other fields
All the carbon nanotubes (CNTs) consist of multiple layer walls and are curved in certain degree
For MCM-41 synthesis, fumed silica was used as Si source and cetyltrimethylammonium chloride (CTACl) as synthetic template. 1.2 g of fumed silica were added into 10.0 g of 45% tetrabutylammonium hydroxide (TBAOH) aqueous solution while vigorously stirring for 30 min to form a transparent gel
Summary
A great attention has been paid to the use of hydrogen on a very large scale in chemicals, food and petroleum refining industries, fuel cell technology, space exploration and other fields. In the steam reforming of hydrocarbons, one of the products, CO, has to be removed by subsequent steps because it strongly poisons the Pt-catalyst which is the key of fuel cell technology. One of the most promising routes for hydrogen production is the direct decomposition of methane, which has the highest hydrogen to carbon ratio in comparison with other hydrocarbon compounds Through this approach, formation of CO can be avoided; the subsequent steps for removal of CO are not necessary. In the methane catalytic decomposition (MCD), if the production of both hydrogen and carbon nanotubes can be effectively combined, we may simultaneously obtain CO-free hydrogen and CNTs by using the same reaction. Ni/MCM-41 catalysts was used for simultaneous production of CO-free hydrogen and CNTs and its catalytic activity and stability were tested in a microreactor using methane as reaction feedstock. Carbon nanotube formation, including its wall thickness, length, diameter and shape was discussed
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