Recently, our Center in collaboration with Prof. Botao Qiao to published communication in Chin Chem Lett. This work focuses on an L-ascorbic acid (AA)-inducing strategy to generate strong metal support interactions (SMSI) on a titania-supported gold (Au) catalyst after high-temperature treatment in an inert atmosphere (600 °C, N₂). The AA-induced SMSI can efficiently stabilize Au nanoparticles (NPs) and preserve their good catalytic performance.

Classical SMSI is one of the most important metal-support interactions which was first discovered by Tauster et al. in 1978 to describe the decrease or loss of chemisorption abilities toward small molecules (CO/H₂) of TiO₂-supported platinum group metals (PGMs) NPs after high-temperature reduction treatment. One of the typical characteristics of the classical SMSI phenomenon is the reduced metal oxide support migrating onto the metal NPs surface to form an encapsulation structure. Therefore, constructing overlayers of SMSI has been widely used to enhance the sinter resistance and high-temperature stability of the supported metal catalysts, especially for the metals with low Tammann temperature and the catalysts used in harsh operating conditions. However, this is often at the cost of activity loss due to the substantial crystalline overlayers, making it difficult for reactants to reach the active sites.

In recent years, numerous studies have focused on developing new routes to construct SMSI at milder conditions including wet chemistry, ultrafast laser, ultra-sonication and mechanochemistry. On the other hand, various adsorbed species induction, rather than the traditional thermally treatment in specific reductive gases (H₂/ CO), can promote the metal catalysts reconstruction. This type SMSI named adsorbate-induced SMSI (A-SMSI) and with the amorphous and permeable encapsulation structure can ensure active metal sites remain accessible. Therefore, it is still desired yet has room to develop new methods to construct SMSI, particularly those facile and universal for a wide range of catalyst systems, to synthesize high-performing catalysts and further understand the formation mechanism of SMSI.

Au/TiO₂ catalyst was synthesized by a deposition-precipitation (DP) method with nominal 5 wt% Au loading on a commercial Degussa P25 support, then modified by AA, followed by heat treatment at 600 °C in an N₂ atmosphere. TEM results shown that Au NPs of Au/TiO₂@AA-N600 samples are covered by a thin layer and homogeneously distributed on the TiO₂, suggesting the introduction of AA is possible to induce the formation of encapsulation. DRIFTS were measured to study the surface structure and adsorption behavior of Au NPs. Despite the existence of the overlayer, the linear CO adsorption signal is still present on Au/TiO₂@AA-N600, which might be due to the existence of gaps/pores on the overlayer supplying channels for CO molecule attaining the gold surface. Au/TiO₂@AA-N600 exhibits outstanding catalytic performance with complete CO conversion at 20 °C even after the high-temperature treatment. Based on the HRTEM results, this surprising activity can be ascribed to the permeable encapsulation of gold by the TiO_x overlayer. Besides, there is no significant deactivation in a 50-hour continuous test, further confirming its good sintering resistance. On the other hand, this strategy could be extended to TiO₂-supported Au catalysts with different crystal phases and platinum group metals, such as Pt, Pd, and Rh.

In summary, for the first time, we have found that the A-SMSI between Au NPs and TiO₂ support can be constructed by L-ascorbic acid adsorption and induction, followed high-temperature treatment at 600 ºC under an inert atmosphere. The unique approach forms permeable TiO_x thin overlayers on the Au NP surface, thus the Au/TiO₂ catalysts with this SMSI can exhibit excellent activity and sintering resistance. This work offers a promising novel route to design stable and efficient
supported noble metal catalysts by constructing SMSI using simple reducing organic adsorbent.

The related research results entitled “Construction of sintering-resistant gold catalysts via ascorbic-acid inducing strong metal-support interactions” has been published in Chinese Chemical Letters. The first author is Yunxia Liu, a doctoral student in our Center. This research is supported by the National Natural Science Foundation of China and the International Partnership Program of the Chinese Academy of Sciences.

Relevant link: https://doi.org/10.1016/j.cclet.2024.110608