Inverse Design of Nanoclusters for Light-Controlled CO2-HCOOH Interconversion

With global push of hydrogen economy, efficient scenarios for hydrogen storage, transportation, and generation are indispensable. Here we devise a strategy for controllable hydrogen fuel storage and retrieval via light-switched CO₂-to-HCOOH interconversion. To realize it, palladium sulfide nanocluster catalysts with multiple specific functionalities are directly searched by our home-developed inverse design approach based on genetic algorithm (IDOGA) and ab initio calculations. Over 500 low-energy Pd_xS_y (x + y ≤ 30) clusters are sieved through a multiobjective function combining stability, activity, optical absorption, and reduction capability of photocarriers. The structure-property relationships and key factors governing the trade-off among these stringent criteria are disclosed. Finally, 14 candidate Pd_xS_y clusters with proper sulfidation degree and high stability in an aqueous environment have been screened. Our IDOGA program provides a general approach for inverse search of nanoclusters with any designated elemental compositions and functionalities for any device applications.

Techniques for the characterization of single atom catalysts

Single atom catalysts (SACs) are a hot research area recently. Over most of the SACs, the singly dispersed atoms are the active sites, which contribute to the catalytic activities significantly compared with a catalyst with continuously packed active sites. It is essential to determine whether SACs have been successfully synthesized. Several techniques have been applied for the characterization of the dispersion states of the active sites over SACs, such as Energy Dispersive X-ray spectroscopy (EDX), Electron Energy Loss Spectroscopy (EELS), etc. In this review, the techniques for the identification of the singly dispersed sites over SACs are introduced, the advantages and limitations of each technique are pointed out, and the future research directions have been discussed. It is hoped that this review will be helpful for a more comprehensive understanding of the characterization and detection methods involved in SACs, and stimulate and promote the further development of this emerging research field.

CO2 Self-Poisoning and Its Mitigation in CuO Catalyzed CO Oxidation: Determining and Speeding up the Rate-Determining Step

Cu-based catalysts are promising for CO oxidation applications with catalyst deactivation being a major barrier. We start with a CuO/Al2O3 catalyst and find that while the CO conversion decreases, CO2 accumulates and the average Cu chemical state stays the same. It suggests CO2 self-poisoning, i.e., CO2 desorption is the rate-determining step. Subsequently, experiments are performed to prove this hypothesis by showing (1) CO2 adsorption inhibits O2 adsorption, (2) complete desorption of CO2 regenerate the catalyst, (3) pre-adsorbed CO2 quenches catalyst activity which recovers during the reaction and (4) the apparent activation energy is consistent with CO2 desorption. It is further evidenced by using a stronger CO2 adsorbing support CeO2 to speed up CO2 desorption from the CuO sites resulting in a superior CuO/CeO2 catalyst. It provides an example for experimentally deciding and speeding up the rate-determining step in a catalytic reaction.

Exploring Cu/Al cluster growth and reactivity: from embryonic building blocks to intermetalloid, open-shell superatoms

Cluster growth reactions in the system [Cu5](Mes)5 + [Al4](Cp*)4 (Mes = mesitylene, Cp* = pentamethylcyclopentadiene) were explored and monitored by in situ LIFDI-MS and 1H-NMR. Feedback into experimental design allowed for an informed choice and precise adjustment of reaction conditions and led to isolation of the intermetallic cluster [Cu4Al4](Cp*)5(Mes) (1). Cluster 1 reacts with excess 3-hexyne to yield the triangular cluster [Cu2Al](Cp*)3 (2). The two embryonic [Cu4Al4](Cp*)5(Mes) and [Cu2Al](Cp*)3 clusters 1 and 2, respectively, were shown to be intermediates in the formation of an inseparable composite of the closely related clusters [Cu7Al6](Cp*)6 (3), [HCu7Al6](Cp*)6 (3H) and [Cu8Al6](Cp*)6 (4), which just differ by one Cu core atom. The radical nature of the open-shell superatomic [Cu7Al6](Cp*)6 cluster 3 is reflected in its reactivity towards addition of one Cu core atom leading to the closed shell superatom [Cu8Al6](Cp*)6 (4), and as well by its ability to undergo σ(C-H) and σ(Si-H) activation reactions of C6H5CH3 (toluene) and (TMS)3SiH (TMS = tris(trimethylsilyl)).

Neutral noble-metal-free VCoO2 and CrCoO2 cluster catalysts for CO oxidation by O2

Neutral noble-metal-free metal oxide cluster catalysts (VCoO₂ and CrCoO₂) were developed for multiple CO oxidation reactions by O₂.