Bao Xinhe, an academician of the Chinese Academy of Sciences, once said that although people know that chemical reactions require catalysts, the principle of "catalysis" of chemical reactions is still poorly understood in the scientific research community. It can be said that it is still a "black box".
Recently, the researcher Fu Qiang of Dalian Institute of Chemical Technology and the team of Academician Bao Xinhe discovered that there is a classic strong metal-support interaction between the transition metal catalyst and the inert hexagonal boron nitride (h-BN) carrier. , SMSI), and the boron nitride carrier shows excellent performance in the dry reforming of methane and carbon dioxide (DRM).
Strong metal-support interaction (SMSI) is a common phenomenon in catalysis science. It means that under a certain atmosphere, the support will migrate and gradually wrap the metal catalyst. The coating formed modifies the adsorption properties and electronic state of the active metal surface, thereby changing the catalyst. The response performance. Most of the time, because the active sites on the surface are covered by the coating, the catalyst in the SMSI state will reduce its efficiency or even fail.
Dry Reforming of Methane (DRM) can simultaneously convert two greenhouse gases into synthesis gas (CO+H2). Ni-based catalysts have both high efficiency and low cost, but they need to be resolved in severe and long-term The problem of catalyst sintering and carbon deposition under reaction conditions.
Boron Nitride Carrier
The low-magnification TEM image of the Ni/h-BN catalyst after 40 hours of reaction is shown in the figure: the average particle size of the nickel particle size distribution is 13.3nm, and the nano pits can be clearly seen around each nickel nanoparticle.
Hexagonal Boron Nitride (h-BN) is stacked sequentially with a layered structure similar to graphene. It has excellent mechanical properties, chemical and thermal stability, and is often used as a protective layer material under extreme conditions. Therefore, in catalysis research, as a carrier, it is taken for granted that it is a material "inert" to the SMSI effect.
However, when the researchers used the h-BN sheet material to support metal Ni nanoparticles, they found that after 40 hours of catalyzing the DRM reaction, the surface of the h-BN nanosheets around the Ni nanoparticles was etched, and many nano-scale pits appeared. It shows that Ni and h-BN have an interaction process in the DRM reaction atmosphere.
Unlike the traditional SMISI effect in which dense oxide encapsulation inhibits the catalytic reaction, the SMSI effect in the h-BN system also has its own uniqueness. Because the oxide of boron is often in an amorphous structure, and the working temperature of the DRM reaction ( 750oC) is also higher than its melting point. Therefore, the BOx covering layer is in an amorphous state under the reaction conditions and has strong fluidity, which may be beneficial for the reactant molecules to contact the metal surface and be activated.
to sum up
The researchers found that only in an atmosphere with a medium oxidizing power such as CO2 and H2O, can the h-BN be etched. No etching occurred in a strong reducing atmosphere (such as H2 and CO), or a strong oxidizing atmosphere (such as O2). The SMSI effect in the h-BN system has a certain universality, and similar phenomena can also be extended to metal catalysts such as Fe, Co, Ru and Pt.
This shows that boron nitride as a catalyst carrier has great potential in specific application scenarios.