Supported atomically dispersed catalysts (SADCs) have attracted extensive attention due to their maximized atom efficiency and unique catalytic performance. Exclusive site homogeneity, distinct energetics and spatial site confinement endow SADCs very attractive in high selectivity and alleviated coke formation in conversion of hydrocarbons, sharply distinct from the low selectivity and heavy coke formation on metal nanoparticle (NP) catalysts.
However, due to the rapid increase in surface free energies, it is a great challenge to obtain catalysts with high loading and high stability under reaction conditions. Among the two standard methods, too strong metal-support interactions (MSIs) may lead to a significant reduction in reactivity, while confinement of the metal species in micropores may limit the mass transfers. Therefore, the rational design of high loading, high stability and high activity SADCs is an urgent matter.
The research team led by Prof. LU prepared a high-loading Ni1Cu2 trimer catalyst on a g-C3N4 support, utilizing the strong metal-support interactions between Cu, Ni atoms and rich nitrogen atoms on the g-C3N4 support, as well as the spatial confinement by Cu atoms. The loading of Ni and Cu were 3.1 wt.% and 8.1 wt.%, respectively.
For semi-hydrogenation of acetylene in excess of ethylene, the prepared Ni1Cu2 trimer catalyst showed excellent catalytic performance in activity, selectivity and stability. The catalyst achieved complete conversion of acetylene at about 170 °C and maintained 90% ethylene selectivity and stability for more than 350 hours.
In situ synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and in situ thermogravimetric analysis (TGA) confirmed that there was almost no coke formation during the hydrogenation reaction. Prof. WEI revealed the coordination structure information of Ni in hydrogen and acetylene hydrogenation atmosphere with the help of in-situ X-ray absorption spectroscopy (XAFS).
In-situ synchrotron radiation vacuum ultraviolet photoionization mass spectrometry and in-situ thermogravimetry showed that there was no carbon deposition in the reaction process. These characterizations indicated that the possible structure of the catalyst is Cu-OH-Ni-OH-Cu. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DIRTFS) of acetylene hydrogenation reaction showed that OH groups were directly involved in the catalytic reaction.
Furthermore, a team led by Prof. LI Weixue from the Dalian Institute of Chemical Physics of CAS determined the spatial configuration of the Cu-OH-Ni-OH-Cu structure through theoretical calculation. The team revealed that the active Ni site confined in two stable hydroxylated Cu grippers changes dynamically by breaking interfacial Ni-support bonds upon reactant adsorption and making these bonds upon product desorption. Such a dynamic effect not only facilitates the acetylene adsorption for high activity, but also ensures high thermal/chemical stability and unprecedented inhibition of coke formation, providing an avenue to rational design of efficient, stable, highly loaded, yet atomically dispersed catalysts.