Structural Evolution of Anatase-Supported Platinum Nanoclusters into a Platinum-Titanium Intermetallic Containing Platinum Single Atoms for Enhanced Catalytic CO Oxidation

Recent Advances of Gaseous Pollutant Catalytic Oxidation over Precious Metal Catalysts with SO2 Exposure

Precious metal catalysts are widely used for catalytic oxidation of various gaseous pollutants (CO, methane, and VOCs) due to their excellent catalytic activity. However, they are easily affected by SO2 and deactivated in actual industrial waste gas or motor vehicle exhaust. Therefore, this review systematically summarizes the representative studies of gaseous pollutant catalytic oxidation over precious metal catalysts with SO2 exposure. First, the sulfur influence mechanisms, including sulfur poisoning and sulfur promotion, as well as the influence of reaction conditions, were discussed to analyze the interaction between SO2 and catalysts and its impact on catalyst properties. Based on the sulfur poisoning process, we further summarized the design strategies of sulfur-resistant catalysts: suppressing the adsorption of SO2 and promoting its desorption, inhibiting the formation of sulfates and facilitating their decomposition, and constructing sacrificial sites, which can be achieved by corresponding design methods: constructing a core-shell/confined structure, dopant modification, and adjusting structural and textural properties. Furthermore, we analyzed feasible catalyst regeneration methods, including N2/O2 atmosphere regeneration, reducing atmosphere-assisted regeneration, and washing regeneration. Finally, the challenges and prospects of the research were proposed, hoping to provide new perspectives on understanding sulfur poisoning processes and guide the design and regeneration of sulfur-resistant catalysts.

Optimizing cooperative catalysis of multiple defective interfaces in Pt/mullite catalysts for NO oxidation

Nitric oxide (NO) oxidation is an integral part of the nitrogen chemical cycle, but competitive activation of NO/O2 over single platinum (Pt)-based catalysts result in inadequate low temperature performance. Here, we constructed catalysts with BiMn2O5/CeO2 and Pt/BiMn2O5 defective interfaces (sufficient activation of NO/O2). The constructed catalyst achieved 95 % NO conversion at 260 °C in NO/O2 atmosphere, superior to most known catalysts. Even after aging (800 °C for 16 h), the NO conversion was up to 76 %. Further, the catalyst can be applied to actual diesel exhaust. Detailed oxygen vacancies (Ov) characterization reveals that BiMn2O5/CeO2 defective interface created by Ce3+-Ov + Mn4+-O ↔ Ce4+-O + Mn3+-Ov promote the activation of NO (on Mn3+ sites) and O2 (on Mn3+-Ov sites). Besides, the Ov on Pt/BiMn2O5 defective interface compensate for the loss of Pt sites ensuring hydrothermal stability. And this construction of multiple defective interfaces develops a pathway for boosting catalytic reactions.

Strong Metal-Support Interaction Triggered by Molten Salts

Strong metal-support interaction (SMSI) plays a vital role in tuning the geometric and electronic structures of metal species. Generally, a high-temperature treatment (>500 °C) in reducing atmosphere is required for constructing SMSI, which may induce the sintering of metal species. Herein, we use molten salts as the reaction media to trigger the formation of high-intensity SMSI at reduced temperatures. The strong ionic polarization of the molten salt promotes the breakage of Ti-O bonds in the TiO2 support, and hence decreases the energy barrier for the formation of interfacial bonds. Consequently, a high-intensity SMSI state is achieved in TiO2 supported Ir nanoclusters, evidenced by a large number of Ir-Ti bonds at the interface, at a low temperature of 350 °C. Moreover, this method is applicable for triggering SMSI in various supported metal catalysts with different oxide supports including CeO2 and SnO2. This newly developed SMSI construction methodology opens a new avenue and holds significant potential for engineering advanced supported metal catalysts toward a broad range of applications.

Electron Delocalization Disentangles Activity-Selectivity Trade-Off of Transition Metal Phosphide Catalysts in Oxidative Desulfurization

Breaking the activity-selectivity trade-off has been a long-standing challenge in catalysis. Here, we proposed a nanoheterostructure engineering strategy to overcome the trade-off in metal phosphide catalysts for the oxidative desulfurization (ODS) of fuels. Experimental and theoretical results demonstrated that electron delocalization was the key driver to simultaneously achieve high activity and high selectivity for the molybdenum phosphide (MoP)/tungsten phosphide (WP) nanoheterostructure catalyst. The electron delocalization not only promoted the catalytic pathway transition from predominant radicals to singlet oxygens in H2O2 activation but also simultaneously optimized the adsorption of reactants and intermediates on Mo and W sites. The presence of such dual-enhanced active sites ideally compensated for the loss of activity due to the nonradical catalytic pathway, consequently disentangling the activity-selectivity trade-off. The resulting catalyst (MoWP2/C) unprecedentedly achieved 100% removal of thiophenic compounds from real diesel at an initial concentration of 2676 ppm of sulfur with a high turnover frequency (TOF) of 105.4 h-1 and a minimal O/S ratio of 4. This work provides fundamental insight into the structure-activity-selectivity relationships of heterogeneous catalysts and may inspire the development of high-performance catalysts for ODS and other catalytic fields.

Simultaneously activating molecular oxygen and surface lattice oxygen on Pt/TiO2 for low-temperature CO oxidation

Developing high-performance Pt-based catalysts with low Pt loading is crucial but challenging for CO oxidation at temperatures below 100 °C. Herein, we report a Pt-based catalyst with only a 0.15 wt% Pt loading, which consists of Pt-Ti intermetallic single-atom alloy (ISAA) and Pt nanoparticles (NP) co-supported on a defective TiO2 support, achieving a record high turnover frequency of 11.59 s-1 at 80 °C and complete conversion of CO at 120 °C. This is because the coexistence of Pt-Ti ISAA and Pt NP significantly alleviates the competitive adsorption of CO and O2, enhancing the activation of O2. Furthermore, Pt single atom sites are stabilized by Pt-Ti ISAA, resulting in distortion of the TiO2 lattice within Pt-Ti ISAA. This distortion activates the neighboring surface lattice oxygen, allowing for the simultaneous occurrence of the Mars-van Krevelen and Langmuir-Hinshelwood reaction paths at low temperatures.

Rutile TiO2-Supported Pt Nanoparticle Catalysts for the Low-Temperature Oxidation of Ethane to Ethanol

Structure-function relationships of supported metal nanoparticle catalysts in the CO-assisted oxidation of ethane to ethanol were investigated. A rutile TiO2-supported Pt nanoparticle catalyst exhibited the highest ethanol production rate and selectivity. During the reaction, sequential changes in the geometric/electronic states and the particle size of the Pt nanoparticles were observed. The comparison of the catalytic performances of model catalysts with controlled metal-support interactions revealed that Pt0 nanoparticles of 2-3 nm with a high fraction of the surface Ptδ+ species are highly active for the oxidation of ethane to ethanol. The coadded CO plays a pivotal role not only in tuning the oxidation state of the surface Pt but also in producing H2O2, which is the true oxidant for the reaction. The supported Pt nanoparticle uses in situ-generated H2O2 to activate ethane, where the C2H5OOH intermediate is formed through a nonradical mechanism and subsequently converted to C2H5OH. This reaction occurs even at 50 °C with an apparent activation energy of 32 kJ mol-1. The present study sheds light on the usefulness of surface-engineered Pt nanoparticles for the low-temperature oxidation of ethane to ethanol.

CO-Assisted Methane Oxidation into Oxygenates over Surface Platinum-Titanium Alloyed Layers

Methane oxidation using molecular oxygen remains a grand challenge in which the obstacle is not only the activation of methane but also the reaction with oxygen, considering the mismatch of the ground spin states. Herein, we report TiO2-supported Pt nanocrystals (Pt/TiO2) with surface Pt-Ti alloyed layers that directly convert methane into oxygenates by using O2 as the oxidant with the assistance of CO. The oxygenate yield reached 749.8 mmol gPt-1 in a H2O aqueous solution over 0.1% Pt/TiO2 under 31 bar of mixed gas (20:5:6 CH4:CO:O2) at 150 °C for 3 h, while the CH3OH selectivity was 62.3%. On the basis of the control experiments and spectroscopic results, we identified the surface Pt-Ti alloy as the active sites. Moreover, CO promoted the dissociation of O2 on the surface of Pt-Ti alloyed layers and the subsequent activation of CH4 to form oxygenated products.

Significance of Epitaxial Growth of PtO2 on Rutile TiO2 for Pt/TiO2 Catalysts

TiO2-supported Pt species have been widely applied in numerous critical reactions involving photo-, thermo-, and electrochemical-catalysis for decades. Manipulation of the state of the Pt species in Pt/TiO2 catalysts is crucial for fine-tuning their catalytic performance. Here, we report an interesting discovery showing the epitaxial growth of PtO2 atomic layers on rutile TiO2, potentially allowing control of the states of active Pt species in Pt/TiO2 catalysts. The presence of PtO2 atomic layers could modulate the geometric configuration and electronic state of the Pt species under reduction conditions, resulting in a spread of the particle shape and obtaining a Pt/PtO2/TiO2 structure with more positive valence of Pt species. As a result, such a catalyst exhibits exceptional electrocatalytic activity and stability toward hydrogen evolution reaction, while also promoting the thermocatalytic CO oxidation, surpassing the performance of the Pt/TiO2 catalyst with no epitaxial structure. This novel epitaxial growth of the PtO2 structure on rutile TiO2 in Pt/TiO2 catalysts shows its potential in the rational design of highly active and economical catalysts toward diverse catalytic reactions.

Electronic Phosphide-Support Interactions in Carbon-Supported Molybdenum Phosphide Catalysts Derived from Metal-Organic Frameworks

Interfacial interaction in carbon-supported catalysts can offer geometric, electronic, and compositional effects that can be utilized to regulate catalytically active sites, while this is far from being systematically investigated in carbon-supported phosphide catalysts. Here, we proposed a novel concept of electronic phosphide-support interaction (EPSI), which was confirmed by using molybdenum phosphide (MoP) supported on nitrogen-phosphorus codoped carbon (NPC) as a model catalyst (MoP@NPC). Such a strong EPSI could not only stabilize MoP in a low-oxidation state under environmental conditions but also regulate its electronic structure, leading to reduced dissociation energy of the oxygen-containing intermediates and enhancing the catalytic activity for oxidative desulfurization. The removal of dibenzothiophene over the MoP@NPC was as high as 100% with a turnover frequency (TOF) value of 0.0027 s-1, which was 33 times higher than that of MoP without EPSI. This work will open new avenues for the development of high-performance supported phosphide catalysts.