Oxidation Of Formaldehyde Research Articles

Selective catalytic oxidation of formaldehyde on single V- and Cr-atom decorated magnetic C4N3 substrate: A first principles study

Formaldehyde (HCHO) is the most common indoor hazardous pollutant and has attracted great concern because its long-term exposure has adverse health effects on humans. Retention and catalytic oxidation of highly hazardous HCHO is an efficient and environmentally friendly method to use for air remediation, but a major obstacle to this procedure is the lack of an appropriate catalyst. Herein, two-dimensional magnetic C4N3 material with a 3d-transition metal as activate sites was systemically investigated in HCHO oxidation using density functional theory calculations. The results show that V-C4N3 and Cr-C4N3 have high structural stability and shallow activation barriers for O2 decomposition; these characteristics provide the necessary precursors for the subsequent oxidation reaction. Moreover, the V-C4N3 and Cr-C4N3 catalysts have unique selective adsorption and catalysis toward HCHO in a mixture of some typical in-door volatile organic compounds (VOCs) and air. The corresponding dynamic barrier for each reaction step was investigated and the mechanism involved in HCHO oxidation was revealed in detail. Aggregation of metal atoms in the V-C4N3 and Cr-C4N3 catalysts is prevented by enormous diffusion resistance, and this is further confirmed by AIMD simulations. These results provide insightful guidance for developing advanced magnetic catalysts for HCHO oxidation to improve the remediation of air contaminants.

Copper oxide and manganese dioxide nanoparticles on corrugated glass-fiber supporters promote thermocatalytic oxidation of formaldehyde

Low catalytic activity and difficult separation of manganese dioxide nanoparticles limit their application in the removal of volatile organic compounds (VOCs). Herein, copper oxide (CuO) and δ-manganese dioxide (MnO2) catalysts were deposited uniformly on a glass-fiber supporter (GFS) by an in-situ precipitation method. The GFS with the hierarchical pores and great specific surface areas was employed as a catalytic supporter. The MnO2 major catalysts and CuO cocatalysts synergistically promoted the formaldehyde thermocatalytic oxidation, and the removal efficiency arrived at nearly 100% even after cycle tests of 4 times. Thermodynamic calculation results demonstrated that the formaldehyde thermocatalytic oxidation over the CuO–MnO2/GFS was performed via a Mars-van Krevelen mechanism. Namely, the formaldehyde molecules were oxidized by the copper oxide and δ-manganese dioxide, and then the as-produced cuprous oxide and manganese sesquioxide were re-oxidized into copper oxide and manganese dioxide by gas phase oxygen. Notably, copper oxide cocatalysts significantly improved the catalytic activity of the CuO–MnO2/GFS because they not only directly participated in the formaldehyde oxidation but also promoted the oxidation reaction of manganese sesquioxide into manganese oxide. This work revealed the synergistic mechanism of MnO2 major catalysts and CuO cocatalysts in promoting thermocatalytic oxidation of formaldehyde, and provided a promising thermocatalyst for the purification of industrial waste gas.

Plasma-engraved Co3O4 nanostructure toward improved formaldehyde oxidation performance: Insight into the structure–activity relationship

Improving the surface area and the number of oxygen vacancy are vital for superior catalytic oxidation performance. Here, plasma-engraved technique was used for surface modification of Co3O4 nanostructure (cube and sphere morphology), which was applied to formaldehyde oxidation reaction. It was found that the formaldehyde oxidation can be boosted over plasma-engraved Co3O4 nanostructure, and efficiently realized at room temperature. Based on varied characterizations, it revealed that the plasma-treatment endowed the Co3O4 nanostructure with surface reconstruction (notches and broken fragments on surface), along with high surface area and rich oxygen vacancies. These factors contribute very important effort for improved activity. Besides, surface reaction mechanism was also proposed based on the in-situ DRIFTs, during which the CHOH was transformed to key intermediates (DOM, formate and/or carbonate), and finally to CO2 and H2O. This study also provides a very efficient strategy for surface modification of heterogeneous solid catalyst and their expand application in environmental catalysis.

Gold-Based Catalysts for Complete Formaldehyde Oxidation: Insights into the Role of Support Composition

Formaldehyde (HCHO) is recognized as one of the most emitted indoor air pollutants with high detrimental effect on human health. Significant research efforts are focused on HCHO removal to meet emission regulations in an effective and economically profitable way. For over three decades, the unique electronic properties and catalytic abilities of nano-gold catalysts continue to be an attractive research area for the catalytic community. Recently, we reported that mechanochemical mixing is a relevant approach to the preparation of Co-Ce mixed oxides with high activity in complete benzene oxidation. A trend of higher surface defectiveness, in particular, oxygen vacancies, caused by close interaction between cobalt oxide and cerium oxide phases, was observed for a mixed oxide composition of 70 wt.% Co3O4 and 30 wt.% CeO2. These results directed further improvement by promotion with gold and optimization of mixed oxide composition, aiming for the development of an efficient catalyst for room temperature HCHO abatement. Support modification with potassium was studied; however, the K addition caused less enhancement of HCHO oxidation activity than expected. This motivated the preparation of new carrier material. In addition to Co3O4-CeO2 mixed metal oxides with preset ratio, γ-Al2O3 intentionally containing 33% boehmite and shortly named Al2O3-b was used for synthesis. Analysis of the role of support composition in HCHO oxidation was based on the characterization of nano-gold catalysts by textural measurements, XRD, HRTEM, XPS, and TPR techniques. Gold supported on mechanochemically treated Co3O4-CeO2-Al2O3-b (50 wt.% Al2O3-b) exhibited superior activity owing to high Ce3+ and Co3+ surface amounts and the most abundant oxygen containing species with enhanced mobility. This catalyst achieved oxidation to CO2 and H2O by 95% HCHO conversion at room temperature and 100% at 40 °C, thus implying the potential of this composition in developing efficient catalytic materials for indoor air purification.

Interfacial dependent reactive oxygen species generation over Pt-ZrO2 nanoparticles for catalytic oxidation of formaldehyde at room temperature

Producing the strong metal-support interaction (SMSI) interface and highly reactive oxygen species is a great challenge for catalytic oxidation of formaldehyde (HCHO) at room temperature over supported metal catalysts. Herein, we report a conceptual oxygen vacancy (VO) associated SMSI interface of Pt-ZrO2 nanoparticles for HCHO catalysis at room temperature, exhibiting interfacial dependent reactive oxygen species (O*) formation. The VO on the ZrO2 support captures and activates the molecular O2, then proceeds to generating the reactive oxygen atom (O*) with a lower activation barrier of 0.3 eV. The generated O* tends to link the (110) surface of ZrO2 and the (111) surface of Pt as an electronic transmission channel for the selective catalytic oxidation of HCHO adsorbed on the (110) surface of ZrO2, accelerating the direct generation of formate species and mineralization of HCHO. The Pt-VO-ZrO2 achieves high HCHO removal and HCHO conversion (>95%) at 20 °C. These findings will consolidate the fundamental theories of room temperature catalytic reactions via constructing the SMSI interface engineering for wide environmental applications.

The effect of hydrogen reduction of α-MnO2 on formaldehyde oxidation: The roles of oxygen vacancies

A series of α-MnO2 catalysts with various Mn valence states were treated by hydrogen reduction for different periods of time. Their catalytic capacity for formaldehyde (HCHO) oxidation was evaluated. The results indicated that hydrogen reduction dramatically improves the catalytic performance of α-MnO2 in HCHO oxidation. The α-MnO2 sample reduced by hydrogen for 2 h possessed superior activity and could completely oxidize 150 ppm HCHO to CO2 and H2O at 70 °C. Multiple characterization results illustrated that hydrogen reduction contributed to the production of more oxygen vacancies. The oxygen vacancies on the catalyst surface enhanced the adsorption, activation and mobility of O2 molecules, and thereby enhanced HCHO catalytic oxidation. This study provides novel insight into the design of outstanding MnOx catalysts for HCHO oxidation at low temperature.

Distinct Role of Surface Hydroxyls in Single-Atom Pt1/CeO2 Catalyst for Room-Temperature Formaldehyde Oxidation: Acid-Base Versus Redox.

The development of highly efficient catalysts for room-temperature formaldehyde (HCHO) oxidation is of great interest for indoor air purification. In this work, it was found that the single-atom Pt1/CeO2 catalyst exhibits a remarkable activity with complete removal of HCHO even at 288 K. Combining density functional theory calculations and in situ DRIFTS experiments, it was revealed that the active OlatticeH site generated on CeO2 in the vicinity of Pt2+ via steam treatment plays a key role in the oxidation of HCHO to formate and its further oxidation to CO2. Such involvement of hydroxyls is fundamentally different from that of cofeeding water which dissociates on metal oxide and catalyzes the acid–base-related chemistry. This study provides an important implication for the design and synthesis of supported Pt catalysts with atom efficiency for a very important practical application—room-temperature HCHO oxidation.

Morphology effects of CeO2 for catalytic oxidation of formaldehyde

Formaldehyde (HCHO) is a primary indoor air pollutant, and can cause serious environmental and health problems. In this study, CeO2 spherical-like aggregate of nanoplates (CeO2-S) were prepared for the HCHO oxidation, and the efficiency of CeO2-S was compared with those of CeO2 nanorods and nanocubes. CeO2-S showed excellent activity, with a maximum HCHO conversion of 87% at 120 °C using a gas hourly space velocity of 10 000 mL·gcat−1·h−1 and HCHO concentration of approximately 500 ppm. The catalysts were characterized using thermal and spectroscopic techniques, revealing that the excellent catalytic performance of CeO2-S originated in its abundant surface hydroxyl and oxygen groups. In situ FT-IR results indicated that dioxymethylene and formates were the main intermediates in HCHO oxidation. Further oxidation of formates produced CO2 and H2O, and CO2 reacted with surface hydroxy groups to form carbonate species, which accumulated on the catalyst surface, thus deactivating the CeO2 catalysts and inhibiting complete conversion of HCHO.

GAS PHASE OXIDATION OF FORMALDEHYDE BY TIO2/TIO2-V2O5/POLYPYRROLE ENERGY STORAGE PHOTOCATALYST

Photocatalytic oxidation of formaldehyde was performed through an electron storage photocatalyst named TiO2/TiO2-V2O5/PPy nanocomposites, consisting of TiO2 responsible for an electron generating source, TiO2-V2O5 functional as an electron storage substance, and PPy (polypyrrole) as an electron conducting substance between the formers. It was found that the TiO2/TiO2-V2O5/PPy nanocomposites showed both adsorption and photocatalytic activity for formaldehyde removal. Under UV irradiation, the catalytic activity of the TiO2/TiO2-V2O5/PPy catalyst was 57%, which was 0.1 and 0.4 times higher than that of TiO2 and TiO2/PPy catalysts, respectively. Moreover, the TiO2/TiO2-V2O5/PPy catalyst retained its function for at least 3 hours, after UV irradiation for 3.5 hours. The presence of TiO2-V2O5 was found to enhance the photocatalytic activity of the TiO2 catalyst, including the ability to function in the absence of UV light. This is due to the lower energy band gap of the TiO2/TiO2-V2O5/PPy, compared to that of TiO2; the TiO2-V2O5 also possesses energy storage ability. Further, the reaction rate of photocatalytic oxidation of formaldehyde by the electron storage photocatalyst was determined. The formaldehyde destruction rate is a function of formaldehyde concentration and can be formulated using a simplified Langmuir-Hinshelwood.

Pathway-Centric Analysis of Microbial Metabolic Potential and Expression Along Nutrient and Energy Gradients in the Western Atlantic Ocean

Microbial communities play integral roles in driving nutrient and energy transformations in the ocean, collectively contributing to fundamental biogeochemical cycles. Although it is well known that these communities are stratified within the water column, there remains limited knowledge of how metabolic pathways are distributed and expressed. Here, we investigate pathway distribution and expression patterns from surface (5 m) to deep dark ocean (4000 m) at three stations along a 2765 km transect in the western South Atlantic Ocean. This study is based on new data, consisting of 43 samples for 16S rRNA gene sequencing, 20 samples for metagenomics and 19 samples for metatranscriptomics. Consistent with previous observations, we observed vertical zonation of microbial community structure largely partitioned between light and dark ocean waters. The metabolic pathways inferred from genomic sequence information and gene expression stratified with depth. For example, expression of photosynthetic pathways increased in sunlit waters. Conversely, expression of pathways related to carbon conversion processes, particularly those involving recalcitrant and organic carbon degradation pathways (i.e., oxidation of formaldehyde) increased in dark ocean waters. We also observed correlations between indicator taxa for specific depths with the selective expression of metabolic pathways. For example, SAR202, prevalent in deep waters, was strongly correlated with expression of the methanol oxidation pathway. From a biogeographic perspective, microbial communities along the transect encoded similar metabolic potential with some latitudinal stratification in gene expression. For example, at a station influenced by input from the Amazon River, expression of pathways related to oxidative stress was increased. Finally, when pairing distinct correlations between specific particulate metabolites (e.g., DMSP, AMP and MTA) and both the taxonomic microbial community and metatranscriptomic pathways across depth and space, we were able to observe how changes in the marine metabolite pool may be influenced by microbial function and vice versa. Taken together, these results indicate that marine microbial communities encode a core repertoire of widely distributed metabolic pathways that are differentially regulated along nutrient and energy gradients. Such pathway distribution patterns are consistent with robustness in microbial food webs and indicate a high degree of functional redundancy.

SnO2 doped NiO heterostructure nanofibers prepared by electrostatic spinning: A novel sensor for catalytic oxidation of formaldehyde

Up to now, there were a large number of literatures on the detection of gaseous formaldehyde (HCHO), however the liquid HCHO, which had the same harmfulness as gaseous HCHO, was rarely paid attention to by people. In this work, the electrospinning nanomaterial preparation process was used to fabricate the liquid HCHO electrochemical sensor. Firstly, five different sets of electrode materials were set up, and the material with the best results (SnO2/NiO NFs (No. 3)) was tested by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV), and electrochemical frequency impedance (EIS). Then the detection principle of the electrochemical sensor and the electrode reaction process of catalytic oxidation of HCHO were analyzed. Finally, the limit of detection (LOD), detection range, selectivity, and stability of the SnO2/NiO NFs (No.3) for the catalytic oxidation reaction of HCHO were analyzed by CV and potential polarization methods.

Manganese Oxide Minerals from the Xiangtan Manganese Deposit in South China and Their Application in Formaldehyde Removal

Because of the nano-scale tunnel constructed by the active Mn-O octahedron in cryptomelane, cryptomelane-type manganese oxides have high activity in the oxidation of several volatile organic compounds (VOCs). Natural cryptomelane, in the form of supergene oxide manganese ore, carpets much of South China. In the lower part of the Datangpo Formation of Nanhua System on the southeastern Yangtze Platform, cryptomelane is one of the major manganese oxides in black shale of the Xiangtan manganese deposit in this deposit. Formaldehyde is a dominant indoor pollutant among volatile organic compounds (VOCs), and applications of synthetic cryptomelane have been reported to eliminate it. To study the removal capacity of naturally outcropping cryptomelane, representative samples of manganese oxide (the primary mineral component of cryptomelane) from the Xiangtan Mn deposit were analyzed in this study. The chemical composition, crystal structure and micromorphology of the manganese oxide minerals were explored using ICP-AES, XRD, EPMA, SEM and HR-TEM techniques. Fine-grained and poorly crystalline, these minerals consist primarily of cryptomelane, along with minor amounts of pyrolusite, hollandite, lithiophorite, limonite and quartz. Natural cryptomelane is a monoclinic crystal, and its cell parameters are refined. The results of catalytic tests revealed that natural cryptomelane has obvious catalytic activity in the oxidation of formaldehyde in a static environment under room temperature. This study may provide a natural mineral material as an inexpensive and efficient catalyst for the purification of formaldehyde in industrial or indoor air treatment.

Electrocatalytic oxidation of formaldehyde using electrospinning porous zein-based polyimide fibers

In this work, electrode coated with electrospinning porous polyimide fibers were prepared. The fiber is made by electrospinning zein from corn by-products and polyacrylic acid (PAA). The prepared porous fiber film was loaded with copper and prepared as working electrode material.The specific surface area of the porous fiber membrane is 304.6313 m2/g. The Polyimide (PI)-Cu nanoparticle electrochemical sensor was prepared by supporting non-noble metal Cu on the porous polyimide for the oxidation of formaldehyde. The prepared electrode can be used to catalyze the oxidation of formaldehyde, and the oxidation peak potential is around −0.41 V. Catalytic oxidation for 300 s at the oxidation peak potential can consume formaldehyde 0.758 × 10−6g, and the coulombic efficiency reaches 74.96%. Electrodes made of cheap metals can quickly remove formaldehyde in solution through electrochemical catalytic oxidation.

Bifunctional zeolites-silver catalyst enabled tandem oxidation of formaldehyde at low temperatures

Bifunctional catalysts with tandem processes have achieved great success in a wide range of important catalytic processes, however, this concept has hardly been applied in the elimination of volatile organic compounds. Herein, we designed a tandem bifunctional Zeolites-Silver catalyst that enormously boosted formaldehyde oxidation at low temperatures, and formaldehyde conversion increased by 50 times (100% versus 2%) at 70 °C compared to that of monofunctional supported silver catalyst. This is enabled by designing a bifunctional catalyst composed of acidic ZSM-5 zeolite and silver component, which provides two types of active sites with complementary functions. Detached acidic ZSM-5 activates formaldehyde to generate gaseous intermediates of methyl formate, which is more easily oxidized by subsequent silver component. We anticipate that the findings here will open up a new avenue for the development of formaldehyde oxidation technologies, and also provide guidance for designing efficient catalysts in a series of oxidation reactions.

Low-temperature oxidative removal of gaseous formaldehyde by an eggshell waste supported silver-manganese dioxide bimetallic catalyst with ultralow noble metal content

Under dark/low temperature (DLT) conditions, the oxidative removal of gaseous formaldehyde (FA) was studied using eggshell waste supported silver (Ag)-manganese dioxide (MnO2) bimetallic catalysts. To assess the synergistic effects between the two different metals, 0.03%-Ag-(0.5–5%)-MnO2/Eggshell catalysts were prepared and employed for DLT-oxidation of FA. The steady-state FA oxidation reaction rate (mmol g-1 h-1), when measured using 100 ppm FA at 80 °C (gas hourly space velocity (GHSV) of 5308 h-1), varied as follows: Ag-1.5%-MnO2/Eggshell-R (9.4) > Ag-3%-MnO2/Eggshell-R (8.1) > Ag-1.5%-MnO2/Eggshell (7.5) > Ag-5%-MnO2/Eggshell-R (7.2) > Ag-1.5%-MnO2/CaCO3-R (6.8) > MnO2-R (6) > Ag-0.5%-MnO2/Eggshell-R (3.2) > Ag/Eggshell-R (2.6). (Here, ‘R’ denotes hydrogen-based thermochemical reduction pretreatment.) The temperature required for 90% FA conversion (T90) at the same GHSV exhibited a contrary ordering: Ag/Eggshell-R (175 °C) > Ag-0.5%-MnO2/Eggshell-R (123 °C) > Ag-5%-MnO2/Eggshell-R (113 °C) > MnO2-R (99 °C) > Ag-1.5%-MnO2/Eggshell (96 °C) > Ag-3%-MnO2/Eggshell-R (93 °C) > Ag-1.5%-MnO2/Eggshell-R (77 °C). The eggshell catalyst outperformed the ones made of commercial calcium carbonate due to the presence of defects in the former. The MnO2 co-catalyst enhances the catalytic activities through the capture and activation of atmospheric oxygen (O2) with rapid catalytic regeneration. Also, MnO2 favorably captures the hydrogen of the adsorbed FA molecules to make the oxidation pathway thermodynamically more favorable.

Reactive adsorption and catalytic oxidation of gaseous formaldehyde at room temperature by a synergistic copper-magnesium bimetal oxide biochar composite

Formaldehyde molecules are actively adsorbed over the copper (glowing blue sphere)-magnesium (glowing green sphere)/biochar (black surface with cracks) to produce formate and carbon dioxide species. The synergistic interaction between copper and magnesium (as depicted by lightning) leads to the enhancement of the overall performance. • Cu-Mg/RH550 oxidized FA into CHOO – and CO 2 through reactive adsorption and catalysis. • Cu-Mg/RH550 showed a maximum adsorption capacity of 10 mg g −1 against 100 ppm FA. • Cu-Mg interaction in bimetallic form lowered their crystallite sizes to enhance activity. • The oxidation of adsorbed FA is expedited via partial reduction of Cu 2+ to Cu + . • Metal oxides host H of FA to make the oxidation reaction thermodynamically feasible. The interactive hybridization of reactive adsorption and catalytic oxidation (RACO) was investigated for the removal of formaldehyde (FA) by fine-tuning the relative compositions of bimetallic oxides between copper (Cu) and magnesium (Mg) on biochar (RH550). The best performer against 100 ppm FA was 8%-Cu-8%-Mg/RH550 when assessed in terms of 10% breakthrough volume (3 L atm g −1 ). The corresponding values for reference materials (e.g., RH550, 16%-Cu/RH550, and 16%-Mg/RH550) were 0.4, 1.1, and 0.5 L atm g −1 , respectively. Adsorption kinetic models confirmed the synergistic roles of physicochemical interactions between the target (FA molecules) and composite material (both organic (RH550) and inorganic (metal oxides) phases). The characterization of the spent Cu-Mg/RH550 suggests that the adsorbed FA molecules were partially oxidized into dioxymethylene and formate. Remarkably, Cu-Mg/RH550 led to the complete room-temperature mineralization of FA into carbon dioxide (CO 2 ) for up to 50 h time-on-stream (artificially set maximum test duration) without any deactivation (gas hourly space velocity of 2,229 h −1 ). The oxidation reaction of FA is expedited by the partial reduction of copper(II) oxide (in Cu-Mg/RH550) to copper(I) oxide. According to the density functional theory-based simulations, the metal oxides make the oxidation reaction thermodynamically favorable by hosting hydrogen abstracted from the adsorbed FA molecules. The Cu-Mg synergy also enhances the capture and activation of molecular oxygen (O 2 ) to boost FA oxidation while sustaining the catalytic process. Overall, this study offers new insights into the synergistic role of RACO in the effective removal of FA under ambient conditions.

Theoretical study of structure sensitivity on Au doped CeO2 surfaces for formaldehyde oxidation: The effect of crystal planes and Au doping

Engineering the surface structure of ceria-based catalysts at the atomic scale is a powerful strategy for boosting catalytic performance. Here, we carried out density functional theory calculations to investigate structure–activity relationships of Au-CeO2 catalysts with (1 1 1), (1 1 0), and (1 0 0) surfaces exposed in common CeO2 nanopolyhedra, nanorods and nanocubes, respectively. On stoichiometric AuCe1-xO2(1 1 1), (1 1 0) and (1 0 0) catalyst surfaces, HCHO oxidation follows the Mars van Krevelen mechanism. Calculations show that the migration of Au atoms on the surface of AuCe1-xO2(1 1 0) leads to a more stable configuration and improved HCHO oxidation performance than the undistorted (1 1 0) surface. On defective AuCe1-xO2(1 1 0) and (1 0 0) surfaces, HCHO oxidation follows the co-action of the Langmuir-Hinshelwood and Mars van Krevelen mechanisms with HCHO and O2 co-participation and surface reduction by the removal of lattice oxygen. Adsorbed O2 species contribute to a decrease in the energy barriers of the reaction steps. With the easy reducibility and lower energy barriers, the defect surfaces are more conducive to HCHO oxidation than stoichiometric surfaces. Whether stoichiometric surfaces or defective surfaces, (1 1 0) is most active for HCHO oxidation with the lowest activation energy for the rate-determining step, followed by (1 1 1), and then (1 0 0). Microkinetic simulations offer additional support for this result. Dopant Au atoms activate surface oxygen, and decrease the formation energy of oxygen vacancies. Au also reduces the energy barriers of key reaction steps on AuCe1-xO2(1 1 1) (1 1 0) (1 0 0) surfaces as compared to the pristine ceria surfaces. These calculations provide insight into the interaction between Au and CeO2 with different surface terminations and the effect of the CeO2 crystal plane and their reactivity for HCHO catalytic oxidation.

Ultra-light 3D MnO2-agar network with high and longevous performance for catalytic formaldehyde oxidation

Under the background of indoor air formaldehyde decontamination, a freestanding ultra-light assembly was fabricated via ice-templating approach starting from MnO2 nanoparticles and environmentally benign agar powder. The 3D composite of agar and MnO2 (AM-3D) was comparatively studied with powdered counterparts (including pure MnO2 and mixture of agar and MnO2) and the 3D-structured agar for formaldehyde oxidation, and their physicochemical properties were examined with XRD, ATR, SEM, XPS, isothermal N2 adsorption, ESR, Raman, CO-TPR and O2-TPD. For the single test of formaldehyde oxidation, the AM-3D catalyst exhibited 62.0%–67.0% removal percentage for ~400 mg/m3 formaldehyde, which did not demonstrate significant advantage over the control samples. However, thanks to the porous 3D agar scaffold with large spatial volume that could promote a rapid gas-phase formaldehyde concentration reduction, and the strong interaction between the dispersed MnO2 particles and agar substrate that could afford a large amount of reactive oxygen species to further oxidize the adsorbed formaldehyde, the AM-3D composite was a much better HCHO-to-CO2 converter and possessed much more advantageous stability for repeated cycles of formaldehyde oxidation: even after ten cycles, there was still 41.7% of formaldehyde removed. Furthermore, the viable sunlight irradiation could easily restore the activity of the used AM-3D catalyst back to the level approaching that of the fresh one. Finally, reaction pathways were put forward via the infrared spectroscopic and ion chromatographic investigations on the surface intermediates of the spent materials.

Two-step hydrothermal synthesis of highly active MnOx-CeO2 for complete oxidation of formaldehyde

MnOx-CeO2 catalysts prepared by either a two-step hydrothermal (HT) method or a deposition–precipitation (DP) method were evaluated for completely oxidation of formaldehyde (HCHO). MnOx-CeO2(HT) exhibited an excellent HCHO oxidation activity. The reaction rate of MnOx-CeO2(HT) was almost six times that of MnOx-CeO2(DP) at 100 °C after excluding the effect of specific surface area. XPS study suggests that MnOx-CeO2(HT) catalyst possessed higher contents of Ce3+ and Mn4+ species than MnOx-CeO2(DP) catalyst due to the synergistic interaction between MnOx and CeO2 (Ce4+ + Mn3+ ↔ Ce3+ + Mn4+). The high Mn4+ content on the surface could provide sufficient HCHO oxidation active sites. The generation of Ce3+ species could lead to abundant chemisorbed oxygen species, which were further determined by in situ DRIFTs, EPR, O2-TPD and H2-TPR studies, and were mainly responsible for the excellent HCHO oxidation activity. DFT simulation also proved these results, which suggests that the Mn loading on CeO2 (110) plane could promote the generation of oxygen vacancy derived from Ce-O-Mn, while the (110) plane was one of the main exposure plane on the surface of Mn-Ce(HT) catalyst. This work provides a simple strategy to design highly active Mn-Ce catalysts for HCHO oxidation. We believe this non-precious catalyst will provide a cost-effective solution for catalytic oxidation of HCHO and other organic pollutants.

The Application of Bi‐Doped TiO2 for the Photocatalytic Oxidation of Formaldehyde

AbstractThe photocatalytic oxidation technology has a great potential for the removal of volatile organic compounds (VOCs). In this research, a novel TiO2/Bi2O3 catalyst is developed to degrade indoor formaldehyde by the photocatalytic oxidation technology. The TiO2/Bi2O3 catalysts with different mass fractions of Bismuth(Bi) are prepared by impregnation method. The characterizations of the TiO2/Bi2O3 catalysts by X‐ray diffraction (XRD), ultraviolet–visible (UV–vis) spectrophotometry, and Brunauer–Emmett–Teller analyses suggest that the doping of TiO2 with Bi neither changes the crystal structure nor the crystal phase of the TiO2, but increases the number of mesopores on the TiO2/Bi2O3 surface and the specific surface area of the TiO2/Bi2O3. By optimizing such parameters as the flow rate; the concentration; and the relative humidity of formaldehyde, the mass fraction of Bi, and the loading amount of the catalyst, a formaldehyde degradation efficiency as high as 96% is obtained.