Subsurface Ru-Triggered Hydrogenation Capability of TiO_2–x Overlayer for Poison-Resistant Reduction of N-Heteroarenes

Abstract

Transition-metal-based catalysts are applied widely in the hydrogenation reaction of different organic compounds. However, serious deactivation occurs when the substrate contains strong coordinating functional groups or impurities. In this paper, we reported that a TiO 2−x overlayer that formed over Ru NPs (Ru@TiO 2−x /TiO 2 ) under reduction conditions worked as a chemoselective, durable, and sulfur-resistant catalyst for the partial hydrogenation of quinoline and other N-heteroarenes. Mechanistic studies revealed that the inhibition of quinoline and its reduced product on the H 2 activation over the Ru NPs was eliminated on the active nonmetal overlayer of Ru@TiO 2−x . The oxygen vacancies of the Ru@TiO 2−x overlayer were determined to be the active sites for H 2 activation. The synergy between the TiO 2 − O v (TiO 2−x ) active sites with the subsurface Ru particles effectively reduced the barriers of H 2 dissociation and H addition steps, enabling the nonmetal TiO 2 −O v shell to catalyze the hydrogenation reaction at mild conditions with remarkable stability and poisoning resistance.

Ultrasonication‐Induced Strong Metal‐Support Interaction Construction in Water Towards Enhanced Catalysis

“…The difference in selectivity is likely modulated by the SMSI overlayer construction since overlayer encapsulation can modulate the surface and electronic properties of the metal NPs via interaction with metal-rich suboxide species resulting in steric hindrance around the active sites. [15,32] However, it should be pointed out that although the encapsulation degree could be tuned by the ultrasonication parameters and solvents resulting in enhanced catalytic activity and selectivity, the controlling capability is still limited compared to other nuanced methods such as reduction oxidationreduction (ROR) where the metal NP surface area can be specifically modulated towards finely tuned catalytic reactions. [65] Therefore, novel and facile methods to afford controllable SMSI constructed catalysts to a greater extent are still of great importance.…”

“…The lifetime existence of cavitation bubbles is remarkably less than a microsecond with heating and cooling rates exemplifying a magnitude of 10 billion °C/s [30, 31] . Notably, generating abundant oxygen vacancies (O v ) in SMSI construction could facilitate the metal oxide overlayer introduction [32–34] . For ultrasonication treatment, several possible avenues exist to create oxygen vacancies.…”

“…As shown in Figure S25, the ultrasonicated sample (Pd/a‐TiO 2 ‐H 2 O‐3h) yields complete conversion to cinnamyl alcohol, while the precursor yields complete conversion to 3‐phenyl‐1‐propanol, 3‐phenylpropanal, and cinnamyl alcohol. The difference in selectivity is likely modulated by the SMSI overlayer construction since overlayer encapsulation can modulate the surface and electronic properties of the metal NPs via interaction with metal‐rich suboxide species resulting in steric hindrance around the active sites [15, 32] . However, it should be pointed out that although the encapsulation degree could be tuned by the ultrasonication parameters and solvents resulting in enhanced catalytic activity and selectivity, the controlling capability is still limited compared to other nuanced methods such as reduction oxidation‐reduction (ROR) where the metal NP surface area can be specifically modulated towards finely tuned catalytic reactions [65] .…”

“…[30] The lifetime existence of cavitation bubbles is remarkably less than a microsecond with heating and cooling rates exemplifying a magnitude of 10 billion °C/ s. [30,31] Notably, generating abundant oxygen vacancies (O v ) in SMSI construction could facilitate the metal oxide overlayer introduction. [32][33][34] For ultrasonication treatment, several possible avenues exist to create oxygen vacancies. First, the collapse of cavitation bubbles can induce high-speed inter-particle collisions and shock waves that produce surface damage increasing oxygen vacancy formation.…”

Palladium Encapsulated by an Oxygen‐Saturated TiO2 Overlayer for Low‐Temperature SO2‐Tolerant Catalysis during CO Oxidation

“…They can attack active precious metals (e.g., Pd, Pt) in catalysts and convert them into stable and inactive metal sulfates, leading to catalyst deactivation. [6] For decades, large efforts have been devoted to solve the problems of sulfur poisoning in many important industrial reactions, e.g., selective catalytic reduction of NO x by NH 3 (NH 3 -SCR), [7][8] CO oxidation, [9][10] N-heteroarenes hydrogenation [11] and fine chemical synthesis. [12] Several strategies based on the "active site protection" concept, such as selective covering of active metal sites, [13][14] regulating metal d-band center, [13,15] and sulfating the oxide support to weaken the adsorption of sulfur species, [16] have been frequently used to improve the sulfur tolerance of metal catalysts.…”