Facet- and defect-engineered Pt/Fe2O3 nanocomposite catalyst for catalytic oxidation of airborne formaldehyde under ambient conditions

Constructing α-MnO2/Mn2O3 heterojunction for formaldehyde oxidation

Constructing heterojunctions with oxygen defect-rich structures and abundant phase interfaces poses an appealing yet challenging task in the development of non-precious metal oxide catalysts for formaldehyde (HCHO) oxidation. Herein, we present a simple and efficient method for fabricating highly active manganese oxide heterojunction catalysts for HCHO oxidation. This method involves the hydrothermal synthesis of a nanostructured α-MnO2/γ-MnOOH composite, followed by mechanical milling-induce phase transformation of γ-MnOOH to Mn2O3. Importantly, mechanical milling not only creates the heterojunction but also imparts oxygen defect-rich structures and an abundant phase interface to the catalyst. The resulting α-MnO2/Mn2O3 heterojunction exhibits outstanding performance in HCHO oxidation, comparable to the best non-precious metal oxide catalysts reported thus far. It achieves a 100% conversion of 100 ppm HCHO under a gas hourly space velocity of 120 L gcat-1 h-1 at 80 °C, corresponding to a mass-specific reaction rate of 8.92 μmol g-1 min-1 and an area-specific reaction rate of 0.18 μmol m-2 min-1. Based on the control experiments using in situ diffuse reflectance infrared Fourier transform spectroscopy combined with online gas chromatography, we gained insights into the mechanism of HCHO oxidation over the α-MnO2/Mn2O3 catalyst and the functional roles played by its component phases.

Room temperature removal of high-space-velocity formaldehyde boosted by fixing Pt nanoparticles into Beta zeolite framework

Catalytic oxidation of volatile organic compounds like formaldehyde (HCHO) over the noble metals catalysts at room temperature is among the most promising strategies to control indoor pollution but remains one challenge to maximize the efficiency of noble metal species. Herein, we demonstrated the straightforward encapsulation of highly dispersive Pt nanoparticles (NPs) within BEA zeolite and adjacent with the surface hydroxyl groups to reach the synergistic HCHO oxidation at 25 °C. High efficiency and long-term stability was reached under large space velocity (∼100% conversion at 180,000 mL (g_cat × h)^-1 and >95% at 360,000 mL (g_cat × h)^-1), affording rapid elimination rate of 129.4 μmol (g_Pt × s)^-1 and large turnover frequency of 2.5 × 10^-2 s^-1. This is the first synergy example derived from the hydroxyl groups and confined noble metals within zeolites that accelerated the rate-determining step, the formate transformation, in the HCHO elimination.

Ozone catalytic oxidation of low-concentration formaldehyde over ternary Mn-Ce-Ni oxide catalysts modified with FeOx

Manganese oxide-based catalysts have attracted extensive attention due to their relatively low cost and remarkable performance for removing VOCs. In this research, we used the Pechini method to synthesize manganese-cerium-nickel ternary oxide catalysts (MCN) and evaluated the effectiveness of catalytic destruction of formaldehyde (HCHO) and ozone at room temperature. FeO_x prepared by the impregnation method was applied to modify the catalyst. After FeO_x treatment, the catalyst represented the best performance on both HCHO destruction and ozone decomposition under dry conditions and exhibited excellent water vapor resistance. The as-prepared catalysts were next characterized via H₂-temperature programmed reduction (H₂-TPR), temperature programmed desorption of O₂ (O₂-TPD), and X-ray photoelectron spectroscopy (XPS), and the results demonstrated that addition of FeO_x increased Mn³⁺ and Ce³⁺ concentrations, oxygen vacancies and surface lattice oxygen species, facilitated adsorption, and redox properties. Based on the results of in situ diffuse reflectance infrared Fourier transform spectrometry (DRIFTS), possible mechanisms of ozone catalytic oxidation of HCHO were proposed. Overall, the ternary mixed-oxide catalyst developed in this study holds great promise for HCHO and ozone decomposition in the indoor environment.

Catalytic performance and mechanism of bismuth molybdate nanosheets decorated with platinum nanoparticles for formaldehyde decomposition at room temperature

Catalytic oxidation at room temperature is considered as a promising strategy for removal of formaldehyde (HCHO), a widely occurring indoor air pollutant. A series of Bi₂MoO₆ nanosheets were prepared via one-step hydrothermal synthesis in this study, followed by decoration with Pt nanoparticles (NPs). The catalyst with Bi₂MoO₆ support prepared at 180 °C exhibited high and stable activity in catalytic oxidation of HCHO at room temperature. The excellent catalytic performance was attributed to its large specific area and pore volume, high level of surface active oxygen species, high content of metallic Pt NPs, and abundant oxygen vacancies. The good synergy and interaction between Pt and Bi₂MoO₆ promoted electron transfer, and facilitated the adsorption and oxidation of HCHO. The electronic interaction between Pt NPs and Bi₂MoO₆ accelerated the activation of oxygen species due to weakening of the surface BiO or MoO bonds adjacent to Pt NPs. Infrared spectra indicated that dioxymethylene and formate species were the main intermediates of HCHO oxidation. Density functional theory calculations showed that the dehydrogenation of HCO₂, with an energy barrier of 282.1 kJ/mol, was the rate-determining step in catalytic oxidation process. This study provides new insights on the construction of high-efficiency catalysts for indoor formaldehyde removal.

Highly Dispersed Pt-Incorporated Mesoporous Fe2O3 for Low-Level Sensing of Formaldehyde Gas

Highly dispersed Pt-incorporated mesoporous Fe₂O₃ (Pt/m-Fe₂O₃) of 4 μm size is prepared through a simple hydrothermal reaction and thermal decomposition procedures. Furthermore, the formaldehyde gas-sensing properties of Pt/m-Fe₂O₃ are investigated. Compared with our previous mesoporous Fe₂O₃-based gas sensors, a gas sensor based on 0.2% Pt/m-Fe₂O₃ shows improved gas response by over 90% in detecting low-level formaldehyde gas at 50 ppb concentration, an enhanced selectivity of formaldehyde gas, and a lower degradation of sensing performance in high-humidity environments. Additionally, the gas sensor exhibits similar properties as the previous sensor, such as operating temperature (275 °C) and long-term stability. The enhancement in formaldehyde gas-sensing performance is attributed to the attractive catalytic chemical sensitization of highly dispersed Pt nanoparticles in the mesoporous Fe₂O₃ microcube architecture.

A room-temperature formaldehyde sensor based on hematite for breast cancer diagnosis

Formaldehyde (HCHO) is regarded as one kind of indoor pollutant. Additionally, HCHO serves as a biomarker in the exhaled breath of breast cancer patients. Early warning and management are crucial for the environment and human health. Thus, we have elaborately synthesized hematite (α-Fe₂O₃) employing a facet-engineering hydrothermal strategy using the fine-tuned solvent composition, with special attention to the effect of different exposed surfaces on HCHO detection. The spindle-like α-Fe₂O₃ nanocrystals with the (012) facet exposed exhibited impressively higher response towards HCHO at room temperature than that of the disk-like α-Fe₂O₃ with mainly the (001) facet exposed, partly due to the abundant vacancy oxygen and adsorbed oxygen of high-index facets of α-Fe₂O₃. More importantly, our experimental results coincide with theoretical calculations. Overall, the surface engineering strategy could be extended to a versatile approach for HCHO detection.

Construction of strongly-coupled CeO2/MnO2 heterogeneous catalysts for highly-efficient removal of formaldehyde

Formaldehyde (HCHO) is highly toxic, but its low-temperature elimination is still a pressing challenge nowadays.

Support Morphology Effect on Selective Hydrogenation of 3-Nitrostyrene to 3-Vinylaniline over Pt/α-Fe2 O3 Catalysts

Selective hydrogenation of substituted nitroaromatic compounds is an extremely important and challenging reaction. Supported metal catalysts attract much attention in this reaction because the properties of metal nanoparticles (NPs) can be modified by the nature of the support. Herein, the support morphology on the catalytic performance of selective hydrogenation of 3-nitrostyrene to 3-vinylaniline was investigated. Pt NPs supported on octadecahedral α-Fe₂ O₃ supports with a truncated hexagonal bipyramid shape (Pt/α-Fe₂ O₃ -O) and rod-shaped α-Fe₂ O₃ supports (Pt/α-Fe₂ O₃ -R) were prepared by glycol reduction method. Detailed characterizations reveal that the electronic structure and dispersion of Pt NPs can be modified by the supports. The Pt/α-Fe₂ O₃ -O catalyst exhibited superior catalytic performance for hydrogenation of 3-nitrostyrene because of its low coordinated Pt sites and the small Pt NPs size, which is benefit from the high-index exposed surfaces of truncated hexagonal bipyramid-shaped α-Fe₂ O₃ support. The structural evolution during the catalytic reaction was investigated in detail by identical location transmission electron microscopy (IL-TEM) method, which found that the high cycling activity of Pt/α-Fe₂ O₃ -O catalyst during the cycle experiment results from the stability of Pt NPs.

High-Index Faceted Nanocrystals as Highly Efficient Bifunctional Electrocatalysts for High-Performance Lithium-Sulfur Batteries

Precisely regulating of the surface structure of crystalline materials to improve their catalytic activity for lithium polysulfides is urgently needed for high-performance lithium-sulfur (Li-S) batteries. Herein, high-index faceted iron oxide (Fe₂O₃) nanocrystals anchored on reduced graphene oxide are developed as highly efficient bifunctional electrocatalysts, effectively improving the electrochemical performance of Li-S batteries. The theoretical and experimental results all indicate that high-index Fe₂O₃ crystal facets with abundant unsaturated coordinated Fe sites not only have strong adsorption capacity to anchor polysulfides but also have high catalytic activity to facilitate the redox transformation of polysulfides and reduce the decomposition energy barrier of Li₂S. The Li-S batteries with these bifunctional electrocatalysts exhibit high initial capacity of 1521 mAh g^-1 at 0.1 C and excellent cycling performance with a low capacity fading of 0.025% per cycle during 1600 cycles at 2 C. Even with a high sulfur loading of 9.41 mg cm^-2, a remarkable areal capacity of 7.61 mAh cm^-2 was maintained after 85 cycles. This work provides a new strategy to improve the catalytic activity of nanocrystals through the crystal facet engineering, deepening the comprehending of facet-dependent activity of catalysts in Li-S chemistry, affording a novel perspective for the design of advanced sulfur electrodes.

Solid-State Dispersions of Platinum in the SnO2 and Fe2O3 Nanomaterials

The dispersion of platinum (Pt) on metal oxide supports is important for catalytic and gas sensing applications. In this work, we used mechanochemical dispersion and compatible Fe(II) acetate, Sn(II) acetate and Pt(II) acetylacetonate powders to better disperse Pt in Fe₂O₃ and SnO₂. The dispersion of platinum in SnO₂ is significantly different from the dispersion of Pt over Fe₂O₃. Electron microscopy has shown that the elements Sn, O and Pt are homogeneously dispersed in α-SnO₂ (cassiterite), indicating the formation of a (Pt,Sn)O₂ solid solution. In contrast, platinum is dispersed in α-Fe₂O₃ (hematite) mainly in the form of isolated Pt nanoparticles despite the oxidative conditions during annealing. The size of the dispersed Pt nanoparticles over α-Fe₂O₃ can be controlled by changing the experimental conditions and is set to 2.2, 1.2 and 0.8 nm. The rather different Pt dispersion in α-SnO₂ and α-Fe₂O₃ is due to the fact that Pt⁴⁺ can be stabilized in the α-SnO₂ structure by replacing Sn⁴⁺ with Pt⁴⁺ in the crystal lattice, while the substitution of Fe³⁺ with Pt⁴⁺ is unfavorable and Pt⁴⁺ is mainly expelled from the lattice at the surface of α-Fe₂O₃ to form isolated platinum nanoparticles.

Engineering oxygen vacancies via amorphization in conjunction with W-doping as an approach to boosting catalytic properties of Pt/Fe-W-O for formaldehyde oxidation

Engineering functional defects in support materials has gained ever-increasing attention as a novel approach to boosting the catalytic performance of oxide-supported catalysts. Herein, we demonstrate the feasibility of engineering oxygen vacancy in iron oxide through amorphization in conjunction with foreign cation doping and elucidate the important role of support functionality in the catalytic oxidation of formaldehyde (HCHO). A supported Pt catalyst on Fe-W-O amorphous nanosheets (denoted as Pt/a-Fe-W-O) was synthesized using a one-step solvothermal method. This simple method allowed us to simultaneously create abundant oxygen vacancies in the substrate and to ensure uniform dispersion of tiny Pt nanoparticles with an average diameter of 1.4 nm on the high-surface-area substrate. This renders an increased possibility of Pt/O-vacancy coexistence in close proximity, which synergistically boosts the formation of active oxygen and surface hydroxyl species. Consequently, the Pt/a-Fe-W-O catalyst with an optimal W/Fe molar ratio of 0.08:1 and a 1.51 wt% Pt loading exhibited a high specific reaction rate of 68.3 μmol g_Pt^-1 s^-1 and excellent stability during 24 h continuous test, outperforming most existing HCHO oxidation catalysts. Our study highlights the importance of functional oxygen defects in construction of synergistic active sites for promoting the reactions requiring multiple active species.

Promotion of TiO2 Nanotube-Confined Pt Nanoparticles via Surface Modification with Fe2O3 for Ethylene Oxidation at Low Temperature

A modified confined catalyst with Pt nanoparticles on the interior and Fe₂O₃ on the exterior surface of TiO₂ nanotubes (Pt-in/Fe₂O₃-TNTs) was prepared and investigated for catalyzing the oxidation of ethylene. Compared with the Pt-in/TNTs without Fe₂O₃ modification, the Pt-in/Fe₂O₃-TNTs exhibited a significantly enhanced activity, and the complete conversion temperature of ethylene decreased from 170 to 95 °C. X-ray photoelectron spectroscopy analysis indicated that the Pt nanoparticles were stabilized at higher oxidation states in the Pt-in/Fe₂O₃-TNT catalyst. It was proposed that the modification of Fe₂O₃ on the outer surface can tune the electronic state of the encapsulated Pt particles and accelerate the electrons transferred from Pt to Fe species via TiO₂ nanotubes, thus improving the catalytic oxidation performance of the confined catalyst.

Polydopamine mediated modification of manganese oxide on melamine sponge for photothermocatalysis of gaseous formaldehyde

It is an urgent need to develop environmentally friendly strategies with low energy consumption for gaseous formaldehyde (HCHO) purification. Herein, a sponge based MS/PDA/MnO_x catalyst with plentiful 3D porosities was constructed. The dual-functional PDA layer not only promoted the MnO_x loading (25 wt% MnO_x in the composite), but also acted as a photothermal converter to absorb photo-irradiation to heat MnO_x catalyst (~80 °C after 10 min irradiation). Moreover, the 3D network structure favored the mass transfer and effectively reduced the catalyst agglomeration to expose more active sites. As a result, the obtained MS/PDA/MnO_x photothermocatalyst showed highly efficient performance for removal of HCHO within concentration of 40-320 ppm at room temperature under xenon light irradiation. This process followed a pseudo-second-order model, and the reaction rate of the MS/PDA/MnO_x was 4.82 times of the MS/MnO_x. Finally, a possible photothermocatalysis mechanism was proposed based on the intermediate examination via the in-situ DRIFTS investigation.

Pt/MnO2 Nanoflowers Anchored to Boron Nitride Aerogels for Highly Efficient Enrichment and Catalytic Oxidation of Formaldehyde at Room Temperature

The catalytic room temperature oxidation of formaldehyde (HCHO) is widely considered as a viable method for the abatement of indoor toxic HCHO pollution. Herein, Pt/MnO₂ nanoflowers anchored to boron nitride aerogels (Pt/MnO₂ -BN) were fabricated for the catalytic room temperature oxidation of HCHO. The three-dimensional Pt/MnO₂ -BN aerogels demonstrated superior catalytic activity as a result of the improved diffusion of the reactant molecules within the porous structure. Furthermore, the porous aerogels displayed excellent HCHO adsorption capacities, which promote a rapid HCHO gas-phase concentration reduction and a subsequent complete oxidation of the adsorbed HCHO. The combined adsorption and oxidation properties of the Pt/MnO₂ -BN aerogels enhance the oxidative removal of HCHO. The optimized Pt/MnO₂ -BN demonstrated excellent catalytic activity toward HCHO (200 ppm) at room temperature, achieving a 96 % formaldehyde conversion after 50 min.

Light-induced synthesis of platinum/titania nanocapsules as an efficient, photosensitive and stable electrocatalyst

Novel Pt/TiO₂ nanocapsules (NCs) having sizes of 40–100 nm and walls of 6–17 nm were successfully synthesized.

Fabrication of Pd/CeO2 nanocubes as highly efficient catalysts for degradation of formaldehyde at room temperature

The highly active Pd/CeO2 nanocube interface guarantees a high percentage of metallic Pd and the surface active O species is responsible for the complete decomposition of formaldehyde.