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Journal ArticleDOI

Advances on transition metal oxides catalysts for formaldehyde oxidation: A review

TL;DR: In this paper, the authors highlight recent advances in the development of transition metal-based catalysts for formaldehyde oxidation, particularly the enhancement of their catalytic activity for low-temperature oxidation, such as morphology and tunnel structures, synthesis methods, specific surface area, amount and type of active surface oxygen species, oxidation state, and density of active sites.
Abstract: This article highlights recent advances in the development of transition metal-based catalysts for formaldehyde oxidation, particularly the enhancement of their catalytic activity for low-temperature oxidation. Various factors that enhance low-temperature activity are reviewed, such as morphology and tunnel structures, synthesis methods, specific surface area, amount and type of active surface oxygen species, oxidation state, and density of active sites are discussed. In addition, catalyst immobilization for practical air purification, reaction mechanism of formaldehyde oxidation, and the reaction parameters affecting the overall efficiency of the reaction are also reviewed.

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Citations
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Journal ArticleDOI
TL;DR: In this paper, a review of recent progress on MnO2-based materials for catalytic oxidation of HCHO, with a particular emphasis on the enhancement of the catalytic activity at low temperature, is presented.

195 citations

Journal ArticleDOI
TL;DR: In this paper, peracetic acid modified coconut shell activated carbon (MnOx/AC) was used for catalytic oxidation of HCHO which is a major indoor air pollutant.

163 citations

Journal ArticleDOI
Jian Ji1, Xiaolong Lu1, Cheng Chen1, Miao He1, Haibao Huang1 
TL;DR: In this paper, a facile redox method was introduced to fabricate a series of MnO2 samples by varying the concentration of K+, which efficiently modulated the layer size, morphology, crystallinity, redox properties, and thus the surface active oxygen species of the obtained δ-MnO2.
Abstract: Engineering MnO2 with rich surface active oxygen species is critical to effectively eliminate formaldehyde (HCHO) under mild conditions. Herein, we introduced a facile redox method to fabricate a series of δ-MnO2 samples by varying the concentration of K+, which efficiently modulated the layer size, morphology, crystallinity, redox properties, and thus the surface active oxygen species of the obtained δ-MnO2. The medium potassium concentration led to the optimized Mn O bond strength, the abundant surface active oxygen species, and the complete conversion of ca. 22 ppm HCHO at 30 °C under a weight hourly space velocity (WHSV) of 200,000 mL/(gcat h). Surface adsorbed oxygen species (e.g., O2− and O−) and surface hydroxyl groups, were suggested to oxidize HCHO into intermediates (i.e., DOM, formate, and carbonate species). Water was critical for further transforming the intermediates into CO2. A Langmuir-Hinshelwood (LH) mechanism was proposed involving in the whole oxidation process.

161 citations

Journal ArticleDOI
Jin Chen1, Dongxu Yan1, Zhen Xu1, Xi Chen1, Wenjian Xu1, Hongpeng Jia1, Jing Chen1 
TL;DR: The characterization of Au/α-MnO2 and catalytic performance tests clearly demonstrate that the proper amount of Au doping facilitates formation of surface vacancy oxygen, lattice oxygen, and charged Au species as an active site, which are all beneficial to catalytic oxidation of HCHO.
Abstract: A novel method of redox precipitation was applied for the first time to synthesize a Au-doped α-MnO2 catalyst with high dispersion of the Au species. Au nanoparticles (NPs) can be downsized into approximate single atoms by this method, thereby realizing highly efficient utilization of Au element as well as satisfying low-temperature oxidation of formaldehyde (HCHO). Under catalysis of the optimal 0.25% Au/α-MnO2 catalyst, a polluted stream containing 500 ppm HCHO can be completely cleaned at 75 °C with the condition of a weight hourly space velocity (WHSV) of 60000 mL/(g h). Meanwhile, the catalyst retains good activity for removal of low-concentration HCHO (about 1 ppm) at ambient temperature with a high WHSV, and exhibits a high tolerance to water and long-term stability. Our characterization of Au/α-MnO2 and catalytic performance tests clearly demonstrate that the proper amount of Au doping facilitates formation of surface vacancy oxygen, lattice oxygen, and charged Au species as an active site, which ...

137 citations

Journal ArticleDOI
TL;DR: The electron spin resonance spectra indicate that the superoxide radical anions photogenerated on the g-C3N4-TiO2/waste zeolites under visible light irradiation are responsible for the decomposition of formaldehyde.

96 citations

References
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Journal ArticleDOI
TL;DR: Adverse health effects from exposure to formaldehyde in prefabricated houses, especially irritation of the eyes and upper airways, were first reported in the mid-1960s and a guideline value of 0.1 ppm was proposed in 1977 by the former German Federal Agency of Health to limit human exposure in dwellings.
Abstract: 1.1. History Formaldehyde was described in the year 1855 by the Russian scientist Alexander Michailowitsch Butlerow. The technical synthesis by dehydration of methanol was achieved in 1867 by the German chemist August Wilhelm von Hofmann. The versatility that makes it suitable for use in various industrial applications was soon discovered, and the compound was one of the first to be indexed by Chemical Abstracts Service (CAS). In 1944, Walker published the first edition of his classic work Formaldehyde.(1) Between 1900 and 1930, formaldehyde-based resins became important adhesives for wood and wood composites. The first commercial particle board was produced during World War II in Bremen, Germany. Since 1950, particle board has become an attractive alternative to solid wood for the manufacturing of furniture. Particle board and other wood-based panels were subsequently also used for the construction of housing. Adverse health effects from exposure to formaldehyde in prefabricated houses, especially irritation of the eyes and upper airways, were first reported in the mid-1960s. Formaldehyde emissions from particle boards bonded with urea formaldehyde resin were soon identified as the cause of the complaints. As a consequence, a guideline value of 0.1 ppm was proposed in 1977 by the former German Federal Agency of Health to limit human exposure in dwellings. Criteria for the limitation and regulation of formaldehyde emissions from wood-based materials were established in 1981 in Germany and Denmark. The first regulations followed in the United States in 1985 or thereabouts. In Germany and the United States, large-scale test chambers were used for the evaluation of emissions. Although the chamber method is very reliable, it is also time-consuming and expensive. This meant there was a strong demand for simple laboratory test methods.(2)

1,253 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of calcination temperature on the structural features and catalytic behavior of the MnO x -CeO 2 mixed oxides prepared by modified coprecipitation was further examined, and the catalyst calcined at 773 K showed 100% formaldehyde conversion at a temperature as low as 373 K.
Abstract: MnO x –CeO 2 mixed oxides prepared by sol–gel method, coprecipitation method and modified coprecipitation method were investigated for the complete oxidation of formaldehyde. Structure analysis by H 2 -TPR and XPS revealed that there were more Mn 4+ species and richer lattice oxygen on the surface of the catalyst prepared by the modified coprecipitation method than those of the catalysts prepared by sol–gel and coprecipitation methods, resulting in much higher catalytic activity toward complete oxidation of formaldehyde. The effect of calcination temperature on the structural features and catalytic behavior of the MnO x –CeO 2 mixed oxides prepared by the modified coprecipitation was further examined, and the catalyst calcined at 773 K showed 100% formaldehyde conversion at a temperature as low as 373 K. For the samples calcined below 773 K, no any diffraction peak corresponding to manganese oxides could be detected by XRD measurement due to the formation of MnO x –CeO 2 solid solution. While the diffraction peaks corresponding to MnO 2 phase in the samples calcined above 773 K were clearly observed, indicating the occurrence of phase segregation between MnO 2 and CeO 2 . Accordingly, it was supposed that the strong interaction between MnO x and CeO 2 , which depends on the preparation route and the calcination temperature, played a crucial role in determining the catalytic activity toward the complete oxidation of formaldehyde.

655 citations


"Advances on transition metal oxides..." refers background or methods or result in this paper

  • ...5 molar ratio being the optimum composition (48,86,93) and the solubility limit for the substitution of Ce ions by Mn ions in the composite (53)....

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  • ...Several conventional preparation methods can be used to synthesize catalysts for HCHO oxidation including sol-gel method (56), precipitation, and coprecipitation (86,97)....

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  • ...(86) indicated that the manifestation of synergy in MnOx-CeO2 solid solution composite, which enables the composite to attain complete HCHO conversion at lower temperature (100°C) compared to pure MnOx and CeO2....

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  • ...The calcination temperature of composite MnOx-CeO2 prepared using modified co-precipitation was shown to greatly influence its catalytic activity for HCHO oxidation (86)....

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  • ...This is in agreement with other reported literatures for the active state of Mn for HCHO oxidation (76,86)....

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Journal ArticleDOI
TL;DR: A novel alkali-metal-promoted Pt/TiO2 catalyst is reported for the ambient destruction of HCHO, significantly promoting the activity for the HCHO oxidation by activating H2O and catalyzing the facile reaction between surface OH and formate species to total oxidation products.
Abstract: Formaldehyde is emitted from building and furnishing materials and consumer products, and is known to cause irritation of eyes and respiratory tract, headache, pneumonia, and even cancer. It is a dominant indoor air pollutant, especially in developing countries, and significant efforts have gone into indoor HCHO purification to meet environmental regulations and human health needs. Removal of HCHO by adsorbents has been investigated extensively using potassium permanganate, activated carbon, aluminum oxide, and some ceramic materials. Sorbent effectiveness is typically limited by low adsorption capacities. Catalytic oxidation is the most effective technology for volatile organic compound (VOC) abatement because VOCs can be oxidized to CO2 over certain catalysts at much lower temperatures than in thermal oxidation. Supported noble metal catalysts (Pt, Pd, Rh, Au, Ag) or metal oxide catalysts (Ni, Cu, Cr, Mn) have been used for the catalytic oxidation of VOCs. Complete oxidation of HCHO over catalysts occurs above 150 8C on clean and oxidized films of Ni, Pd, and Al and over silver–cerium composite oxide, above 100 8C over Ag/MnOx-CeO2 [18] and Au/CeO2, [19] and above 85 8C over Pd-Mn/Al2O3 [17] and Au/FeOx. As catalytic oxidation at even lower temperatures is desirable for indoor air purification, the development of a catalyst for total HCHOoxidation at room temperature is of great interest. In our recent study, 1% Pt/TiO2 catalyst was shown to be effective for HCHO oxidation at room temperature, achieving 100% conversion of d= 100 ppm HCHO to CO2 and H2O at a gas hourly space velocity (GHSV) of 50000 h . However, we also observed that this type catalyst is not as active as needed for practical applications, and deactivates with time-on-stream. Herein, we report a novel alkali-metal-promoted Pt/TiO2 catalyst for the ambient destruction of HCHO. We show that the addition of alkali-metal ions (such as Li, Na, and K) to Pt/TiO2 catalyst stabilized an atomically dispersed PtO(OH)x–alkali-metal species on the catalyst surface and also opened a new low-temperature reaction pathway, significantly promoting the activity for the HCHO oxidation by activating H2O and catalyzing the facile reaction between surface OH and formate species to total oxidation products. Figure 1a shows the HCHO conversion to CO2 as a function of temperature over the x% Na-1% Pt/TiO2 (x= 0, 1, and 2) samples at a GHSVof 120000 h 1 andHCHO inlet of d= 600 ppm. All gas streams were humidified to a RH of around 50%. Before each activity test, the samples were reduced in H2 at 300 8C for 30 min. The sodium-free catalyst had low activity for the HCHO oxidation reaction, with HCHO conversion being only about 19% at 15 8C. With 1% Na addition, the HCHO conversion reached 96% at 15 8C and 100% at 40 8C. With 2% Na addition, 100% HCHO conversion to CO2 and H2O was measured at 15 8C. The effect of Na addition on the surface reducibility was examined by H2 temperature-programmed reduction (TPR; Figure 1b). The amounts of H2 consumption were about the same over all the samples, but the addition of Na shifted the reduction peak to lower temperatures, that is, from 2 8C for 1% Pt/TiO2 to 6 8C for 1% Na-1% Pt/TiO2 and 11 8C for 2% Na-1% Pt/ TiO2. Thus, the sample reducibility correlates with the sample activity. The most active 2% Na-promoted sample had excellent stability as checked by long isothermal tests. For example, at a GHSV of 300000 h 1 and with the same other reaction conditions, approximately 80% HCHO conversion was maintained over a 72 h-long test (Figure 1a, inset). Li and K were equally effective promoters to Na and imparted the same high activity and stability to the Pt species (Supporting Information, Figure S1). Water vapor and oxygen effects on the activity of Na-Pt/TiO2 are important (Supporting Information, Figures S2,S3). Deionized-water washing of the samples was performed to check the alkali-metal and Pt interaction.While most of the Na was removed from the Nacontaining catalysts, a residual amount remained (Supporting Information, Table S1). Activity test results (Supporting Information, Figure S1) showed that the washed catalyst had identical activity for HCHO [*] C. Zhang, F. Liu, Y. Liu, Prof. H. He Research Center for Eco-Environmental Sciences Chinese Academy of Sciences Shuangqing Road 18, Beijing, 100085 (China) E-mail: honghe@rcees.ac.cn

592 citations

Journal ArticleDOI
TL;DR: In this paper, a simplified mechanism for the catalytic oxidation of formaldehyde (HCHO) over 1% Pt/TiO2 was proposed, based on the behavior of adsorbed species on the surface at room temperature using in situ DRIFTS.
Abstract: The performance of TiO2 supported noble metal (Pt, Rh, Pd and Au) catalysts was examined and compared for the catalytic oxidation of formaldehyde (HCHO). Among them, the Pt/TiO2 was the most active catalyst. The effects of Pt loading and gas hourly space velocity (GHSV) on Pt/TiO2 activity for HCHO oxidation were investigated at a room temperature (20 degrees C). The optimal Pt loading is 1 wt.%. At this loading, HCHO can be completely oxidized to CO2 and H2O over the Pt/TiO2 in a GHSV of 50,000 h(-1) at 20 degrees C. The 1% Pt/TiO2 was characterized using BET, XRD, high resolution (HR) TEM and temperature programmed reduction (TPR) methods. The XRD patterns and HR TEM image show that Pt particles on TiO2 are well dispersed into a size smaller than 1 nm, an important feature for the high activity of the 1% Pt/TiO2. The mechanism of HCHO oxidation was studied with respect to the behavior of adsorbed species on Pt/TiO2 surface at room temperature using in situ DRIFTS. The results indicate that surface formate and CO species are the main reaction intermediates during the HCHO oxidation. The formate species could decompose into adsorbed CO species on the catalyst surface without the presence Of O-2, and the CO was then oxidized to CO, with the presence of O-2. Based on these results, a simplified mechanism for the catalytic oxidation of HCHO over 1% Pt/TiO2 was proposed. (c) 2006 Elsevier B.V. All rights reserved.

502 citations

Journal ArticleDOI
TL;DR: In this paper, the structure, synthesis, host-guest reaction in aqueous phase, and ion-sieve and molecular sieve properties of porous manganese oxide crystals are reviewed.
Abstract: This article reviews the structure, synthesis, host-guest reaction in aqueous phase, and ion-sieve and molecular-sieve properties of porous manganese oxide crystals. Tunnel and layered manganese oxides constitute a large family of porous materials having pore size from ultramicropores to mesopores. The manganese oxide crystals consist of MnO 6 octahedral units shared by corners and/or edges. They can be prepared by using various metal ions or organic surfactants as templates. The templates are extracted/inserted topotactically from/into the tunnels or interlayer spaces of the manganese oxides by two different mechanisms: redox-type and ion-exchange-type. These manganese oxides show excellent ion-sieve and molecular-sieve properties for the adsorptions of cations or organic molecules. The adsorptive selectivities are dependent on their structures.

453 citations


"Advances on transition metal oxides..." refers background in this paper

  • ...Manganese oxide-based catalysts Manganese oxide is the most widely explored transition metal catalyst for HCHO oxidation owing to its high catalytic activity, thermal stability, existence in various crystal morphologies such as α-, β-, γ-, and δ-MnOx (71) and several tunnel assemblies (1D tunnels, layered structures such as birnessite and buserite and 3D spinel tunnel structures) (72)....

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