Room-temperature HCHO Oxidation Research Articles

The Promoting Effect of Metal Vacancy on CoAl Hydrotalcite-Derived Oxides for the Catalytic Oxidation of Formaldehyde

Formaldehyde (HCHO) is a major harmful volatile organic compound (VOC) that is particularly detrimental to human health indoors. Therefore, effectively eliminating formaldehyde is of paramount importance to ensure indoor air quality. In this study, CoAl hydrotalcite (LDH) was prepared using the co-precipitation method and transformed into composite metal oxides (LDO) through calcination. Additionally, a metal Al vacancy was constructed on the surface of the composite metal oxides (EX-LDO and EX-LDO/NF) using an alkaline etching technique. SEM demonstrated the successful loading of CoAl-LDO onto nickel foam surfaces (LDO/NF), and an extended etching time resulted in a greater number of porous structures in the samples. XRD confirmed the successful synthesis of the precursor materials, CoAl hydrotalcite (CoAl-LDH) and CoAl layered double oxides (CoAl-LDO). EDS analysis confirmed a reduction in aluminum content after alkaline etching. XPS analysis verified the presence of abundant Co2+ and surface oxygen as crucial factors contributing to the catalyst’s excellent catalytic activity. The experimental results indicated that catalysts containing metal cation vacancies exhibited superior catalytic performance in formaldehyde oxidation compared to conventional hydrotalcite-derived composite oxides. H2-TPR confirmed a significant enhancement in the participation of lattice oxygen in the catalytic oxidation reaction; it was found that the proportion of surface lattice oxygen consumption by the E5-LDO catalyst (30.2%) is higher than that of the LDO catalyst (23.4%), and the proportion of surface lattice oxygen consumption by the E1-LDO/NF catalyst (27.5%) is higher than that of the LDO/NF catalyst (14.6%), suggesting that cation vacancies can activate the surface lattice oxygen of the material, thereby facilitating improved catalytic activity. This study not only reveals the critical role of surface lattice oxygen in catalytic oxidation activity, but also aids in the further development of novel catalysts for efficient room-temperature oxidation of HCHO. Moreover, it provides possibilities for developing high-performance catalysts through surface modification.

Pt single atoms and defect engineering of TiO2-nanosheet-assembled hierarchical spheres for efficient room-temperature HCHO oxidation

Achieving high atomic utilization and low cost of desirable Pt/TiO2 catalysts is a major challenge for room temperature HCHO oxidation. Here, the strategy of anchoring stable Pt single atoms by abundant oxygen vacancies over TiO2-nanosheet-assembled hierarchical spheres (Pt1/TiO2-HS) was designed to eliminate HCHO. A superior HCHO oxidation activity and CO2 yield (∼100% CO2 yield) at relative humidity (RH) > 50% over Pt1/TiO2-HS is achieved for long-term run. We attribute the excellent HCHO oxidation performance to the stable isolated Pt single atoms anchored on the defective TiO2-HS surface. The Ptδ+ on the Pt1/TiO2-HS surface has a facile intense electron transfer with the support by forming Pt-O-Ti linkages, driving HCHO oxidation effectively. Further in situ HCHO-DRIFTS revealed that the dioxymethylene (DOM) and HCOOH/HCOO- intermediates were further degraded via active OH- and adsorbed oxygen on the Pt1/TiO2-HS surface, respectively. This work may pave the way for the next generation of advanced catalytic materials for high-efficiency catalytic HCHO oxidation at room temperature.

Unravelling the critical role of silanol in Pt/SiO2 for room temperature HCHO oxidation: An experimental and DFT study

In the present work, Pt/SiO2 catalysts have been prepared by impregnating as-prepared Pt NPs onto commercial SiO2 of tailored silanol density (2.3, 3.1 and 4.5 OH nm−2) produced through hexamethyldisilazane passivation. The resulting Pt/SiO2 catalysts were then tested for formaldehyde (HCHO) total oxidation. The catalytic tests showed that high surface silanol density led to lower apparent activation energy (from 40.7 kJ⸱mol−1 at 2.3 OH nm−2 to 21.9 kJ⸱mol−1 at 4.5 OH nm−2)), allowing formaldehyde total oxidation in dry and wet conditions (100% conversion into CO2 over Pt/SiO2 (4.5 OH nm−2) at room temperature in dry condition, among the best catalytic performances reported). DFT calculations described the different interaction behaviours of HCHO, H2O, CO and CO2 on pure SiO2 and Pt/SiO2 (1.1–7.2 OH nm−2) surface, showing the critical role of silanols in the total oxidation of formaldehyde over Pt/SiO2 in different humid conditions.

Room temperature HCHO oxidation over the Pt/CeO2 catalysts with different oxygen mobilities by changing ceria shapes

Oxygen mobility contributes to HCHO oxidation at room temperature. In this work, oxygen mobilities of the Pt/CeO2 catalysts were controlled by changing ceria shapes to nanorods (CeO2-R), nanocubes (CeO2-C) and nanoparticles (CeO2-P) for HCHO elimination. The smallest ceria crystallite size, the strongest metal-support interaction and the most oxygen vacancy in the Pt/CeO2-R catalyst than those in the Pt/CeO2-C and Pt/CeO2-P catalysts resulted in the greatest redox of surface lattice oxygen and the most oxygen molecules activation at oxygen vacancy sites. These contributed to the most active mobile oxygen and therefore the highest HCHO oxidation performance. In-situ diffused reflectance infrared Fourier-transform spectra (DRIFT) indicated the fastest decomposition of formate at Pt-CeO2 interface on the Pt/CeO2-R catalyst because of its highest oxygen mobility. This work illustrated importance of oxygen mobility for efficient HCHO oxidation.

Preparation of flexible Pt/TiO2/γ-Al2O3 nanofiber paper for room-temperature HCHO oxidation and particulate filtration

A flexible Pt/TiO2/γ-Al2O3 nanfiber paper (PTA) was successfully prepared by an electrospinning-coating-NaBH4 reduction method. The catalytic performance for formaldehyde (HCHO) oxidation over PTA with different Pt contents was investigated at room temperature. The results show that PTA exhibits higher catalytic activity and stability than Pt/γ-Al2O3. The TiO2 coating can promote the transformation of intermediate species and the desorption of CO2. The PTA1 with 1 wt% Pt shows the best catalytic activity and good stability. In the view of activity and cost, 0.5 wt% Pt is the optimal Pt content. The TiO2 coating not only plays an important role in improving the activity and stability of PTA, but also acts as a protective shell of γ-Al2O3 fiber, which greatly reduces the risk of alkali etching during preparation and maintains the good flexibility of PTA. The dioxymethylene (DOM), formate/carbonate species, CO are the intermediate species in HCHO oxidation over PTA. In addition, PTA exhibits good filtration performance for fine particles as well as good fluid permeability. Because of the high efficiency and flexibility of PTA composite catalytic material for HCHO oxidation with good filtration performance for fine particles, it will be a promising candidate in air purification.

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

AbstractThe 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.

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.

Oxygen vacancy–engineered δ-MnOx/activated carbon for room-temperature catalytic oxidation of formaldehyde

Although oxygen vacancies (OVs) commonly act as adsorption/active sites in catalytic oxidation of formaldehyde (HCHO), thereby strongly influencing catalyst activity, their control and translation into scale-up products for practical application remain challenging. Herein, δ-MnOx/activated carbon was synthesized via in situ reduction coupled with ammonia modification, and the developed method was found to allow easy OV control for large-scale production. OV concentration was effectively regulated through adjustment of Mn3+ content, and OV roles in the catalytic reaction were probed by several techniques. The optimized catalyst featured superior HCHO removal efficiency and CO2 selectivity at room temperature, mainly due to oxygen activation by abundant OVs to form reactive oxygen species. The intermediates and pathways of HCHO removal were investigated. Thus, this work provides insights into the enhancement of active site exposure through OV control for a single bulk catalyst and demonstrates its applicability for efficient and commercially viable room-temperature oxidation of HCHO.

Effect of alkali metal auxiliary in HCHO oxidation on the model catalyst Na2O/Pd(1 1 1): A DFT study

Alkali metal over noble-metal based catalyst could significantly promote room-temperature HCHO oxidation. Understanding alkali metal auxiliary effects from a molecular level is vital for improving the design of the catalytic oxidation catalysts. The electronic interaction between Na2O and the Pd(1 1 1) surface and HCHO oxidation mechanism on these model catalysts have been investigated using periodic density functional theory (DFT) calculations. The results showed the Pd(1 1 1) are negatively charged after Na2O introduction derived from electron transfer between Na2O and Pd(1 1 1). The adsroption ability of Na2O/Pd(1 1 1) increased, resulting in the enhancement of the interactions between reactants and Pd-based catalyst. Furthermore, the possible reaction pathways for HCHO oxidation on the Pd(1 1 1) and Na2O/Pd(1 1 1) surface were also evaluated inorder to elucidate the role of alkali Na. The generation of dioxymethylene and formate intermediates is the only way for HCHO oxidation whether with or without Na2O auxiliary. Unlike on the pure Pd catalyst, the formate will directly decompose into CO2 via the modulation of alkali metal. The function of alkali-metal auxiliary is not only modulating the electronic state of primary catalyst, but also includes taking part in the actual reaction.

Hierarchical NiMn2O4/rGO composite nanosheets decorated with Pt for low-temperature formaldehyde oxidation

Graphene nanomaterials can improve the textural properties and surface reactivity of metal-based HCHO oxidation catalysts, leading to improved room-temperature HCHO oxidation performance.

Cobalt nanoparticles encapsulated in porous nitrogen-doped carbon: Oxygen activation and efficient catalytic removal of formaldehyde at room temperature

The removal of carcinogenic formaldehyde (HCHO) to improve indoor air quality has attracted significant attention. Designing efficient catalysts for practical HCHO oxidation without use of noble metals remains challenging. In this study, metallic Co nanoparticles were encapsulated with porous nitrogen-doped carbon (Co@NC). This catalyst achieved HCHO elimination at room temperature for the first time. The as-prepared Co@NC catalyst exhibited superior catalytic activity (>80%) for HCHO removal compared with the oxidized one, and possessed the excellent stability. Theoretical calculations showed that the metallic Co in Co@NC is the active site for O2 dissociation, which enhanced the catalytic activity compared to traditional transition-metal oxides, such as Co3O4 with the high-valence state Co3+ providing active sites. The formate species was the main intermediate, which was further oxidized to CO2 as the final product. Hence, an efficient non-noble-metal catalyst for room-temperature HCHO oxidation was developed.

Graphene oxide/Fe2O3 nanoplates supported Pt for enhanced room-temperature oxidation of formaldehyde

Graphene oxide (GO)/Fe2O3 nanoplates supported Pt catalyst (Pt/GOFe) for room-temperature oxidation of formaldehyde (HCHO) was obtained via hydrothermal synthesis of Fe2O3 nanoplates, impregnation of GO and Pt precursor and NaBH4 reduction processes. Compared with TiO2 supported Pt (Pt/TiO2), Fe2O3 nanoplates supported Pt (Pt/Fe) and GO/commercial Fe2O3 supported Pt (Pt/GOFe-c), Pt/GOFe exhibited much higher catalytic activity toward room-temperature HCHO oxidation. The superior catalytic performance of Pt/GOFe is attributed to the unique morphology of Fe2O3 nanoplates, abundance of oxygen functionalities and the mobility of ππ bonds of GO, as well as plenty of active oxygen species resulted from the interaction between Pt and GO/Fe2O3. The in-situ DRIFTS results revealed that the surface hydroxyls played an important role in HCHO oxidation reaction, and formate/DOM species were the main intermediates. The excellent catalytic performance and recyclability make Pt/GOFe an efficient catalyst for HCHO oxidation at room temperature, which sheds a new light on rational design and fabrication of advanced catalyst for indoor air purification.

Heterostructured Fe2O3@SnO2 core–shell nanospindles for enhanced Room-temperature HCHO oxidation

Heterostructures combining structural and compositional merits of individual building blocks are promising in advanced catalysis for environmental remediation. We herein report a facile construction of Fe2O3@SnO2 core–shell nanospindles via assembly of SnO2 shells over Fe2O3 cores. With loading of trace Pt nanoparticles, the Pt/Fe2O3@SnO2 shows enhanced room-temperature HCHO oxidation activity to the Pt/Fe2O3 and Pt/SnO2. Density Function Theory (DFT) simulations demonstrate the synergetic effects of the Fe2O3 and SnO2 in the Fe2O3@SnO2, with the Fe2O3 cores facilitating adsorption/activation of reactant O2 and the SnO2 shells promoting desorption of reactant H2O. The present study highlights advantages of heterostructure and provides a rational design strategy for advanced catalysts.

Active oxygen species adsorbed on the catalyst surface and its effect on formaldehyde oxidation over Pt/TiO2 catalysts at room temperature; role of the Pt valence state on this reaction?

Pt/TiO2 catalysts, prepared by reduction pretreatment, showed enhanced catalytic activities in formaldehyde oxidation. X-ray photoelectron spectroscopy analysis confirmed that catalytic activity was affected by Pt valence states in the Pt/TiO2 catalyst. Using O2 re-oxidation tests, we showed that there was a correlation between the area of oxygen consumed and the ratio of metallic Pt species on the catalyst surface. The O2 re-oxidation ability was involved in the production of the adsorbed formate intermediate from HCHO, confirmed through diffuse reflectance infrared Fourier transform spectroscopy analysis. Furthermore, metallic Pt species were involved in the oxidation of adsorbed CO to CO2.

Oriented growth of layered-MnO2 nanosheets over α-MnO2 nanotubes for enhanced room-temperature HCHO oxidation

Construction of heterostructures with well-defined size, dimension, surface and interface is an effective approach to develop enhanced and unprecedented functionality. Herein, oriented growth of layered-MnO2 nanosheets (L-MnO2) over α-MnO2 nanotubes backbones is demonstrated. The epitaxial relationship in the resulting α-MnO2@L-MnO2 heteroepitaxy is rationalized as (110)(α-MnO2)||(001)(layered-MnO2). With loading of 1wt% Pt nanoparticles over the MnO2 samples, the resulting Pt/MnO2 samples show catalytic activity toward room-temperature HCHO oxidation via “HCHO+O2=CO2+H2O”. Upon 1h treatment, 92.1% HCHO becomes mineralized over the Pt/α-MnO2@L-MnO2, higher than that of 81.3% and 75.9% for the Pt/α-MnO2 and Pt/L-MnO2. The oxidation of HCHO was well fitted with the second-order kinetic model, with the rate constant of the Pt/α-MnO2@L-MnO2 exceeding that of the Pt/α-MnO2 and the Pt/L-MnO2 by 2.27 and 5.92 times. Density-Functional-Theory (DFT) simulations show that α-MnO2 {100} surface facilitates adsorption/activation of O2, and layered-MnO2 {001} surface is beneficial to desorption of resultant H2O. The α-MnO2@L-MnO2 heteroepitaxy simultaneously integrates exposed facets of α-MnO2 {100} surface and layered-MnO2 {001} surface, in which the synergetic effect of the two surfaces leads to significantly enhanced room-temperature HCHO oxidation activity. The present study provides a rational design of manganese oxide-based catalysts for advanced environmental and energy applications.

Efficient formaldehyde oxidation over nickel hydroxide promoted Pt/γ-Al2O3 with a low Pt content

Rational design of efficient noble metal catalysts and its application process by the interface promoted strategy is an emerging research field. Herein, highly efficient nickel hydroxide promoted PtNi(OH)x/γ-Al2O3 catalysts for room temperature HCHO oxidation was developed. PtNi(OH)x/γ-Al2O3 demonstrates remarkably better performance than the state of the art non-reductive oxide supported Pt catalysts, and ranges among the best performance of the reductive metal oxide supported Pt catalysts. A (>)99% HCHO conversion and a (>)100h stable performance at 30°C were obtained over PtNi(OH)x/γ-Al2O3 with a 0.3wt% Pt loading amount. Various characterizations, including in situ DRIFTS study, were performed to understand the reason for the enhanced performance of PtNi(OH)x/γ-Al2O3. The superior performance is attributed to the formation of enormous Pt/Ni(OH)x interface, and the preferred hydroxyl facilitated HCHO oxidation pathway through formate oxidation by the abundant associated hydroxyl groups nearby the Pt active sites. Such hydroxyl groups confined interface promotion strategy may bring new insight into the designing of highly efficient bimetallic catalysts and its potential technological applications for HCHO removal.