Highly Stable Pt/CeO2 Catalyst with Embedding Structure toward Water-Gas Shift Reaction

Active Interfacial Perimeter in Pt/CeO2 Catalysts with Embedding Structure for Water-Tolerant Toluene Combustion

Supported Pt catalysts are often subjected to severe deactivation under the conditions of high temperature and water vapor in catalytic oxidation; thus, the superior stability and water-resistant ability of catalysts have great significance for the effective degradation of volatile organic compounds (VOCs). Herein, we constructed a Pt/CeO2-N catalyst with an active interfacial perimeter, in which Pt species were partially embedded in the defective CeO2-N support to prevent the sintering. A significant charge transfer between Pt species and ceria in the embedding structure occurred via the Pt-CeO2 interface, which induced the formation of a Pt4+-Ov-Ce3+ interfacial structure. Experimental research and theoretical calculations demonstrated that the active Pt4+-Ov-Ce3+ interface promoted the activation and migration of lattice oxygen, thus facilitating the participation of oxygen species in toluene oxidation. Consequently, Pt/CeO2-N showed excellent catalytic performance for toluene degradation. In situ DRIFTS and DFT calculation proved that the Pt4+-Ov-Ce3+ interfacial sites served as the intrinsic active center in the dissociation of H2O to generate ·OH, which contributed to the formation of benzaldehyde, thus remarkably improving the water-resistant property. This study provided a facile strategy for fabricating the interfacial embedding structure to enhance the catalytic activity and water tolerance for eliminating VOCs in practical application.

Metal-Independent Correlations for Site-Specific Binding Energies of Relevant Catalytic Intermediates

Establishing energy correlations among different metals can accelerate the discovery of efficient and cost-effective catalysts for complex reactions. Using a recently introduced coordination-based model, we can predict site-specific metal binding energies (ΔE M) that can be used as a descriptor for chemical reactions. In this study, we have examined a range of metals including Ag, Au, Co, Cu, Ir, Ni, Os, Pd, Pt, Rh, and Ru and found linear correlations between predicted ΔE M and adsorption energies of CH and O (ΔE CH and ΔE O) at various coordination environments for all the considered metals. Interestingly, all the metals correlate with one another under specific surface site coordination, indicating that different metals are interrelated in a particular coordination environment. Furthermore, we have tested and verified for PtPd- and PtIr-based alloys that they follow a similar behavior. Moreover, we have expanded the metal space by taking some early transition metals along with a few s-block metals and shown a cyclic behavior of the adsorbate binding energy (ΔE A) versus ΔE M. Therefore, ΔE CH and ΔE O can be efficiently interpolated between metals, alloys, and intermetallics based on information related to one metal only. This simplifies the process of screening new metal catalyst formulations and their reaction energies.

Effect of H2O and CO2 on CO oxidation over Pt/SSZ-13 with active sites regulated by Lewis acidity

Strategies for controlling the size of metal species using zeolites and their catalytic behavior in industrially relevant processes have attracted widespread attention, but the effect of H2O and CO2 on the catalytic performance of zeolite-based metal catalysts remains obscure. This study investigated the influence of H2O and CO2 on CO oxidation over zeolite-based metal catalysts, along with the precise control of active sites through the regulation of Lewis acidity. It was found that the presence of H2O enhanced CO oxidation and alleviated the inhibitory effect of CO2. Abundant Lewis acid sites of low SiO2/Al2O3 ratios in the Pt/SSZ-13 catalyst facilitate Pt dispersion (61.07%), a high Ptn+/Pt ratio (4.43), and small Pt particles (2.31 nm) formation. In situ DRIFTS revealed that CO2 inhibits CO adsorption and the decomposition of carbon intermediates. Water alters the CO adsorption configuration of Pt0, thereby weakening the Pt-CO bond to promote the CO oxidation reaction. Meanwhile, water dissociated into hydroxyl groups on the surface adsorbs oxygen species, participating in reactions and promoting CO2 production from carbon intermediates. H218O isotope labeling experiments validated the water involvement in the reaction and emphasized the importance of the presence of oxygen species during the water dissociation process. Regulation of Lewis acid sites promotes the Ptn+ species formation, enhancing the CO oxidation activity, while Pt0 species enhance the water-promotion effect.

Ceria-based supported metal catalysts for the low-temperature water-gas shift reaction

Water-gas shift (WGS) reaction is a crucial step for the industrial production of hydrogen or upgrading the hydrogen generated from fossil or biomass sources by removing the residual CO. However, current industrial catalysts for this process, comprising Cu/ZnO and Fe2O3-Cr2O3, suffer from safety or environmental issues. In the past decades, ceria-based materials have attracted wide attention as WGS catalysts due to their abundant oxygen vacancies and tunable metal-support interaction. Strategies through engineering the shape or crystal facet, size of both metal and ceria, interfacial-structure, etc., to alter the performances of ceria-based catalysts have been extensively studied. Additionally, the developments in the in situ techniques and DFT calculations are favorable for deepening the understanding of the reaction mechanism and structure-function relationship at the molecular level, comprising active sites, reaction path/intermediates, and inducements for deactivation. This article critically reviews the literature on ceria-based catalysts toward the WGS reaction, covering the fundamental insight of the reaction path and development in precisely designing catalysts.

Single-Atom Barium Promoter Enormously Enhanced Non-Noble Metal Catalyst for Ammonia Decomposition

As a well-established topic, single-atom catalyst has drawn growing interest for its high utilization of metal. However, researchers prefer to develop various active metals with single-atom form, the intrinsic roles of single-atom promoters are usually underrated, which are significant in boosting reaction activity. In this work, Ba single atoms were in situ prepared in the Co-Ba/Y2O3 catalyst with crystallized BaCO3 as the precursor under the ammonia decomposition reaction condition. The optimized Co-Ba/Y2O3 catalyst achieves extremely high H2 production rate of 138.3 mmolH2 ⋅ gcat -1 ⋅ min-1 at very low temperature (500 °C, GHSV=840,000 mL ⋅ g-1 ⋅ h-1) and Co-Ba/Y2O3 exhibits excellent durability during the 350 h test, which realizes the highest activity among all non-noble catalysts, and reaches or even exceeds numerous reported Ru-based catalysts. Both Y2O3 and Co demonstrate positive interactions with Ba, which significantly facilitates the dispersion of Ba species at high temperatures (≥600 °C). Ba single atoms significantly enhance the charge density of Co and form additionally active Co-O-Ba-Y2O3 interfacial sites, which alleviates hydrogen poisoning and decreases the reaction barrier of the N-H bond activation of *NH. The exploration of atomically dispersed promoters is groundbreaking in heterogeneous catalysis, which opens up a whole new domain of catalytic material.

Exploring the Impact of Oxygen Vacancies in Co/Pr-CeO2 Catalysts on H2 Production via the Water-Gas Shift Reaction

In this study, we utilized various Pr-doped CeO2 catalysts (Pr=5, 10, 20, and 30 wt.%) as a support medium for the dispersion of cobalt (Co) nanoparticles, aiming to investigate the impact of oxygen vacancies on the water-gas shift (WGS) reaction. Different characterization techniques were employed to understand the insights into the structure-activity relationship governing the performance of Pr doped ceria supported Co catalysts towards WGS reaction. Our findings reveal that Co/Pr-CeO2 catalysts at optimum Pr loading (10 wt.%) exhibit a superior CO conversion (88 %) facilitated by the presence of more oxygen vacancies induced by Pr doping into the CeO2 lattice, as opposed to the performance of the pure Co/CeO2 catalytic system. It was also found that the highest activity was obtained at increased intrinsic oxygen vacancies and strong synergy between Co and Pr/CeO2 support, fostering more favorable CO activation at the interfacial sites, thus accounting for the observed enhanced activity.

Engineering Asymmetric Strain within C-Shaped CeO2 Nanofibers for Stabilizing Sub-3 nm Pt Clusters against Sintering

Ultrafine noble metals have emerged as advanced nanocatalysts in modern society but still suffer from unavoidable sintering at temperatures above 250 °C (e.g., Pt). In this work, closely packed CeO2 grains were confined elegantly in fibrous nanostructures and served as a porous support for stabilizing sub-3 nm Pt clusters. Through precisely manipulating the asymmetry of obtained nanofibers, uneven strain was induced within C-shaped CeO2 nanofibers with tensile strain at the outer side and compressive strain at the inner side. As a result, the enriched oxygen vacancies significantly improved adhesion of Pt to CeO2, thereby boosting the sinter-resistance of ultraclose sub-3 nm Pt clusters. Notably, no aggregation was observed even after exposure to humid air at 750 °C for 12 h, which is far beyond their Tammann temperature (sintering onset temperature, below 250 °C). In situ HAADF-STEM observation revealed a unique sintering mechanism, wherein Pt clusters initially migrate toward the grain boundaries with concentrated stain and undergo slight coalescence, followed by subsequent Ostwald ripening at higher temperatures. Moreover, the sinter-resistant Pt/C-shaped CeO2 effectively catalyzed soot combustion (over 700 °C) in a durable manner. This work provides a new insight for developing sinter-resistant catalysts from the perspective of strain engineering within nano-oxides.

Stabilizing ultra-close Pt clusters on all-in-one CeO2/Al2O3 fibril-in-tubes against sintering

Metal sintering poses significant challenges for developing reliable catalytic systems toward high-temperature reactions, particularly those based on metal clusters with sizes below 3 nm. In this work, electrospun dual-oxide fibril-in-tubes consisting of CeO2 and Al2O3 are rationally designed in an all-in-one manner, to stabilize 2.3 nm Pt clusters with a Tammann temperature (sintering onset temperature) lower than 250 °C. The abundant pores and channels effectively stabilize the Pt clusters physically, while the strong support, CeO2, with high adhesion, pins Pt clusters firmly, and the adjacent weak support, Al2O3, with low adhesion, provides energy barriers to prevent the clusters and emitted Pt atom(s) from moving across the support. Therefore, the ultra-close 2.3 nm Pt clusters, featuring an average nearest neighboring distance of only 2.1 nm, were carefully stabilized against sintering at temperatures exceeding 750 °C, even in oxidative and steam-containing environments. In addition, this catalytic system can efficiently and durably serve in diesel combustion, a high-temperature exothermic reaction, showing no activity decline after 5 cycles. This work provides a comprehensive understanding of sinter-resistant catalytic systems, and presents new insights for the development of advanced nanocatalysts.

Exploring the Facet-Dependent Structural Evolution of Pt/CeO2 Catalysts Induced by Typical Pretreatments for CO Oxidation

Atomic-scale insights into the interactions between metals and supports play a crucial role in optimizing catalyst design, understanding catalytic mechanisms, and enhancing chemical conversion processes. The effects of oxide support on the dynamic behavior of supported metal species during pretreatments or reactions have been attracting a lot of attention; however, very less systematic integrations are carried out experimentally using real catalysts. In this study, we here utilized facet-controlled CeO2 as examples to explore their influence on the supported Pt species (1.0 wt %) during the reducing and oxidizing pretreatments that are typically applied in heterogeneous catalysts. By employing a combination of microscopy, spectroscopy, and first-principles calculations, it is demonstrated that the exposed crystal facets of CeO2 govern the evolution behavior of supported Pt species under different environmental conditions. This leads to distinct local coordinations and charge states of the Pt species, which directly influence the catalytic reactivity and can be leveraged to control the catalytic performance for CO oxidation reactions.

Low Temperature NO and CO Conversion with a Mechanistic Approach on Ru-Composed Cerium Oxide

Catalytic reduction of NO with CO at a lower temperature is an extremely challenging task, thus requiring conceivable surfaces to overcome such issues. Ru-substituted CeO2 catalysts prepared via the solution combustion method were employed in CO oxidation and NO-CO conversion studies. The characterization for material formation and surface structure was carried out through XRD, SEM, TEM, and BET surface area. The catalytic study revealed the promising behavior of 5% Ru in CeO2 for the 100% conversion of NO-CO at 150 °C, proving it to be an excellent exhaust material. These observed results are also supported by temperature-programmed studies, i.e. TPD of NO and CO in addition to NH3-TPD and H2-TPR for their convincible surface interaction that is inclined toward a significant change in the conversion path. Additionally, the proposed mechanism, based on the experimental evidence, sheds light on the NO-CO redox reaction, directing the reaction pathway toward the Langmuir-Hinshelwood and Mars-Van Krevelen-type route. Moreover, the exceptional performance can be attributed to the strategic incorporation of Ru in CeO2, where the strong interaction of Ru-Ce is able to gain a high synergy for NO and CO conversion.

Tuning the Metal-Support Interaction by Modulating CeO2 Oxygen Vacancies to Enhance the Toluene Oxidation Activity of Pt/CeO2 Catalysts

In this research, a range of Pt/CeO2 catalysts featuring varying Pt-O-Ce bond contents were developed by modulating the oxygen vacancies of the CeO2 support for toluene abatement. The Pt/CeO2-HA catalyst generated a maximum quantity of Pt-O-Ce bonds (possessed the strongest metal-support interaction), as evidenced by the visible Raman results, which demonstrated outstanding toluene catalytic performance. Additionally, the UV Raman results revealed that the strong metal-support interaction stimulated a substantial increase in oxygen vacancies, which could facilitate the activation of gaseous oxygen to generate abundant reactive oxygen species accumulated on the Pt/CeO2-HA catalyst surface, a conclusion supported by the H2-TPR, XPS, and toluene-TPSR results. Furthermore, the results from quasi-in situ XPS, in situ DRIFTS, and DFT indicated that the Pt/CeO2-HA catalyst with a strong metal-support interaction led to improved mobility of reactive oxygen species and lower oxygen activation energies, which could transfer a large number of activated reactive oxygen species to the reaction interface to participate in the toluene oxidation, resulting in the relatively superior catalytic performance. The approach of tuning the metal-support interaction of catalysts offers a promising avenue to develop highly active catalysts for toluene degradation.

Schottky Barrier-Based Built-In Electric Field for Enhanced Tumor Photodynamic Therapy

Photodynamic therapy's antitumor efficacy is hindered by the inefficient generation of reactive oxygen species (ROS) due to the photogenerated electron-hole pairs recombination of photosensitizers (PS). Therefore, there is an urgent need to develop efficient PSs with enhanced carrier dynamics. Herein, we designed Schottky junctions composed of cobalt tetroxide and palladium nanocubes (Co3O4@Pd) with a built-in electric field as effective PS. The built-in electric field enhanced photogenerated charge separation and migration, resulting in the generation of abundant electron-hole pairs and allowing effective production of ROS. Thanks to the built-in electric field, the photocurrent intensity and carrier lifetime of Co3O4@Pd were approximately 2 and 3 times those of Co3O4, respectively. Besides, the signal intensity of hydroxyl radical and singlet oxygen increased to 253.4% and 135.9%, respectively. Moreover, the localized surface plasmon resonance effect of Pd also enhanced the photothermal conversion efficiency of Co3O4@Pd to 40.50%. In vitro cellular level and in vivo xenograft model evaluations demonstrated that Co3O4@Pd could generate large amounts of ROS, trigger apoptosis, and inhibit tumor growth under near-infrared laser irradiation. Generally, this study reveals the contribution of the built-in electric field to improving photodynamic performance and provides new ideas for designing efficient inorganic PSs.

New insight into the catalytic mechanism of ester hydrogenation over the Cu/ZnO catalyst: the contribution of hydrogen spillover

The dimethyl maleate hydrogenation activity of Cu, ZnO-X and physically mixed Cu+ZnO-X samples was systematically investigated to probe the essential role of ZnO in ester hydrogenation processes. Cu samples exhibited high CC bond hydrogenation ability with dimethyl succinate as the main product. Comparatively, ZnO was inactive in hydrogenation due to its weak ability to dissociate hydrogen while the CO group could be activated and adsorbed on the ZnO surface. Interestingly, physical mixing with ZnO significantly improved the CO hydrogenation activity of Cu samples. The H2-TPD results reveal the origin of "Cu-ZnO synergy": hydrogen atoms formed on the copper surface can spill over to the ZnO surface and react with the adsorbed CO group.