Low-temperature Oxidation Of Formaldehyde Research Articles

Insight into formaldehyde decomposition over MOFs-derived CeO2-MnOx bimetallic oxides

The ubiquitous presence of formaldehyde as a pollutant has aroused significant environmental and health concerns. The design and performance of (OR: transition metal oxide) catalysts in the catalytic oxidation method continue to face a myriad of challenges. Herein, a series of CeO2-x-MnOx catalysts are synthesized using manganous nitrate impregnated Ce-metal–organic-frameworks as the precursor, followed by a traditional calcination step. Interestingly, we found that the gases released during the pyrolysis of metal–organic-frameworks significantly affect the valence states of Ce and Mn, which are key factors responsible for catalytic activity. Characterizations results show that the CeO2-x-MnOx-2.5 sample contains a large amount of Ce3+, a high Mn3+/Mn4+ ratio, and an abundance of reactive oxygen species on its surface. Density functional theory results demonstrate that oxygen vacancies not only effectively suppress charge loss of Mn and Ce atoms but also significantly enhance the adsorption strength of CeO2-x-MnOx-2.5 for both formaldehyde and O2. These structural features jointly influence the adsorption as well as the rapid oxidation of formaldehyde molecules, leading to the excellent catalytic performance towards formaldehyde oxidation. This study provides a promising platform for designing straightforward, cost-effective, and highly efficient bimetallic catalysts suitable for low-temperature formaldehyde oxidation.

Structure-Function Relationship of Highly Reactive CuOx Clusters on Co3 O4 for Selective Formaldehyde Sensing at Low Temperatures.

Designing reactive surface clusters at the nanoscale on metal-oxide supports enables selective molecular interactions in low-temperature catalysis and chemical sensing. Yet, finding effective material combinations and identifying the reactive site remains challenging and an obstacle for rational catalyst/sensor design. Here, the low-temperature oxidation of formaldehyde with CuOx clusters on Co3 O4 nanoparticles is demonstrated yielding an excellent sensor for this critical air pollutant. When fabricated by flame-aerosol technology, such CuOx clusters are finely dispersed, while some Cu ions are incorporated into the Co3 O4 lattice enhancing thermal stability. Importantly, infrared spectroscopy of adsorbed CO, near edge X-ray absorption fine structure spectroscopy and temperature-programmed reduction in H2 identified Cu+ and Cu2+ species in these clusters as active sites. Remarkably, the Cu+ surface concentration correlated with the apparent activation energy of formaldehyde oxidation (Spearman's coefficient ρ = 0.89) and sensor response (0.96), rendering it a performance descriptor. At optimal composition, such sensors detected even the lowest formaldehyde levels of 3 parts-per-billion (ppb) at 75°C, superior to state-of-the-art sensors. Also, selectivity to other aldehydes, ketones, alcohols, and inorganic compounds, robustness to humidity and stable performance over 4 weeks are achieved, rendering such sensors promising as gas detectors in health monitoring, air and food quality control.

Construction of Supported MnOx/MgAl Hydrotalcite Catalysts and Their Highly Efficient Catalytic Performance for Low-Temperature Formaldehyde Removal

A series of supported MnOx/MgAl-layered double hydroxide (LDH) catalysts were prepared by hydrothermal co-precipitation to investigate their catalytic performances for low-temperature formaldehyde oxidation reactions. Activity tests show that the 10Mn/Mg3Al1-LDH catalyst exhibits higher efficiency for low-temperature formaldehyde oxidation with a high CO2 yield. It also shows remarkable long-term operational stability as well as good adaptability to different velocities and humidities. Various characterizations were carried out to establish the possible structure–activity correlations. The results show that there were a large number of hydroxyl groups in the 10Mn/MgAl-LDH catalysts, and the hydroxyl groups were positively correlated with Mg2+ content. The outstanding catalytic performance of 10Mn/Mg3Al1-LDH can be attributed to abundant surface hydroxyl groups, surface adsorbed oxygen and higher Mn4+/Mn3+ ratios. Through in situ Fourier-transform infrared spectroscopy (in situ FTIR), it was revealed that formaldehyde was gradually converted into CO2 and water with dioxymethylene (DOM), formate and carbonate as the major intermediates under the action of both active oxygen and active hydroxyl groups. The active oxygen and active hydroxyl groups consumed in the process are continuously replenished by the effective reaction between the oxygen molecules in the air and the active site of the catalyst. The low-temperature asynchronous conversion of formaldehyde results in the accumulation of some intermediates on the catalyst surface covering the active center, which induces catalyst deactivation.

High-pressure steam treatment with Pt/TiO2 enhances the low temperature formaldehyde oxidation performance

A facile high-pressure steam treatment is developed to improve the formaldehyde oxidation performance of the typical Pt/TiO2 catalyst at low temperatures. The formaldehyde oxidation rate of the treated Pt/TiO2 catalyst can be increased by 4.8 times compared with that of the pristine one. Simultaneously, the treated Pt/TiO2 catalyst possesses the good catalytic stability and catalytic resistance to dry environment. The kinetic study shows that formaldehyde molecules are more liable to be oxidized on the treated Pt/TiO2. A series of characterization results display that the structural parameters of Pt and TiO2 treated with high-pressure steam are not altered. It is found that a layer of bound water is formed on the surface of Pt nanoparticles, which can modify some surface properties of treated Pt/TiO2 catalyst. The interaction strength of intermediates (e.g. CO) with Pt is significantly weakened. Moreover, the amounts of oxygen species and surface hydroxyl for HCHO oxidation are dramatically increased on the treated Pt/TiO2. Based on these characteristics, two reaction steps of formate and CO can be accelerated to enhance the low temperature HCHO oxidation performance of treated Pt/TiO2 catalyst according to the HCHO-DRIFTS studies.

Cerium modified birnessite-like MnO2 for low temperature oxidation of formaldehyde: Effect of calcination temperature

Cerium modified birnessite-like MnO2 were synthesized (CexMn; x = 0.01; 0.1) from a simple and inexpensive redox method involving the reduction of potassium permanganate by sodium lactate in the presence of Ce(NO3)3 at ambient temperature. The as-synthesized samples were calcined at different temperatures (Tc: 200, 300 and 400 °C) to be tested in HCHO total oxidation in dry air at low temperature. The Ce0.01Mn catalyst calcined at 400 °C showed the best catalytic activity in HCHO oxidation with a T50 (temperature at which 50 % of HCHO was converted into CO2) of 50 °C and was found to be air and moisture stable (up to 75 %RH) upon time. The beneficial effects of a calcination step at 400 °C allowed to get enhanced asymmetric Ce-O-Mn surface interactions along with highly dispersed Ce4+/3+ related species and enhanced TCMn3+ (TC: triple corner) amounts which contributed to a great extent for its high activity in HCHO oxidation.

Opposite Effects of Co and Cu Dopants on the Catalytic Activities of Birnessite MnO2 Catalyst for Low-Temperature Formaldehyde Oxidation

Defect engineering is an effective strategy to enhance the activity of catalysts for various applications. Herein, it was demonstrated that in addition to enhancing surface properties via doping, t...

Low-temperature formaldehyde oxidation over manganese oxide catalysts: Potassium mediated lattice oxygen mobility

Manganese oxide catalysts with self-modulating K+ content and tunable concentration of lattice oxygen and Mn4+ were synthesized and investigated for HCHO oxidation. The preparation method affects the physicochemical properties and catalytic activity of the catalysts. Herein, the role of K+ in enhancing the lattice oxygen mobility of manganese oxide catalysts for enhanced formaldehyde (HCHO) is presented. The presence of K+ enhances the redox properties of Mn and promotes catalytic activity by enhancing the mobility of the lattice oxygen and sustaining the availability of surface active oxygen to sustain the reaction. Catalytic activity was observed to improve with increasing K+ content and the surface concentration of lattice oxygen and Mn4+. A drastic reduction in catalytic activity was observed in the acid-treated samples, with low K+ concentration. Characterization results indicate that the presence of K+ enhances activity and mobility of the lattice oxygen by the weakening the Mn-O bond in manganese oxide and promotes the redox properties of the catalyst. The absence of K+ impacted the mobility of the lattice oxygen and the ability of the catalyst to supplement the consumed oxygen species, resulting into reduced catalytic activity and deactivation in the room-temperature (30 °C) activity and stability test.

Catalytic activity of niobium oxide supported bimetallic nanocatalysts (IrxPt1-x/Nb2O5) for oxidation of formaldehyde at moderate temperature

Niobium oxide (Nb2O5) nanoparticles supported bimetallic nanocatalysts (IrxPt1-x/Nb2O5) for low temperature formaldehyde oxidation were obtained. The as-synthesized IrxPt1-x/Nb2O5 nanocatalysts exhibited higher activities and stability than bare Nb2O5 for catalytic formaldehyde oxidation. The Ir:Pt ratio have considerable effects on the activity of the nanocatalyst, and the Ir0.5Pt0.5/Nb2O5 has the highest catalytic activity among all the Nb2O5 supported bimetallic nanocatalysts, and the temperature for 100% formaldehyde oxidation reached as low as 30 °C. The catalytic stability of Ir0.5Pt0.5/Nb2O5 nanocatalyst exhibited that after four reaction cycles and no catalyst deactivation was detected after 36 h operation.

MnO2-decorated N-doped carbon nanotube with boosted activity for low-temperature oxidation of formaldehyde

Low-temperature oxidative degradation of formaldehyde (HCHO) using non-noble metal catalysts is challenging. Herein, novel manganese dioxide (MnO2)/N-doped carbon nanotubes (NCNT) composites were prepared with varying MnO2 content. The surface properties and morphologies were analyzed using X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM). Comparing with MnO2/carbon nanotubes (CNTs) catalyst, the 40% MnO2/NCNT exhibited much better activity and selectivity for HCHO oxidation, mineralizing 95% of HCHO (at 100 ppm) into CO2 at 30 °C at a gas hourly space velocity (GHSV) of 30,000 mL h-1 g-1. Density functional theory (DFT) calculation was used to analyze the difference in the catalytic activity of MnO2 with CNTs and NCNT carrier. It was confirmed that the oxygen on NCNT was more active than CNTs, which facilitated the regeneration of MnO2. This resulted in remarkably boosted activity for HCHO oxidation. The present work thus exploited an inexpensive approach to enhance the catalytic activity of transition metal oxides via depositing them on a suitable support.

Highly dispersed Fe–Ce mixed oxide catalysts confined in mesochannels toward low-temperature oxidation of formaldehyde

Highly dispersed Fe–Ce mixed oxides confined in mesochannels are prepared by two-step impregnation–calcination, achieving superior catalytic oxidation of HCHO (9.8 μg L−1) with 65 and 94.9% at 30 and 60 °C, respectively.

MOF-derived metal oxide composite Mn2Co1Ox/CN for efficient formaldehyde oxidation at low temperature

A novel MOF-derived MnCoOx nanoparticles embedded in porous N-doped carbon catalyst exhibits excellent catalytic activity for the low-temperature oxidation of formaldehyde.

A Novel Redox Precipitation to Synthesize Au-Doped α-MnO2 with High Dispersion toward Low-Temperature Oxidation of Formaldehyde.

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 are all beneficial to catalytic oxidation of HCHO. The oxidation of HCHO over Au-doped α-MnO2 catalyst obeys the Mars-van Krevelen mechanism as evidenced by in situ diffuse reflectance infrared Fourier transform spectroscopy.

Achieving low temperature formaldehyde oxidation: A case study of NaBH4 reduced cobalt oxide nanowires

Oxygen vacancies enable the formation of reactive oxygen species (O2−), which can react with the HCHO absorbed at the catalysts surfaces. As a result, the Co3O4 nanowires with surface oxygen vacancies demonstrated superior catalytic performance for HCHO oxidation and exhibited excellent stability in long-term test.

A highly durable catalyst based on Co x Mn3–x O4 nanosheets for low-temperature formaldehyde oxidation

Cost-effective catalysts for the oxidation of volatile organic compounds (VOCs) are critical to energy conversion applications and environmental protection. The main bottleneck of this process is the development of an efficient, stable, and cost-effective catalyst that can oxidize HCHO at low temperature. Here, an advanced material consisting of manganese cobalt oxide nanosheet arrays uniformly covered on a carbon textile is successfully fabricated by a simple anodic electrodeposition method combined with post annealing treatment, and can be directly applied as a high-performance catalytic material for HCHO elimination. Benefiting from the increased surface oxygen species and improved redox properties, the as-prepared manganese cobalt oxide nanosheets showed substantially higher catalytic activity for HCHO oxidation. The catalyst completely converted HCHO to CO2 at temperatures as low as 100 °C, and exhibited excellent catalytic stability. Such impressive results are rarely achieved by non-precious metal-based catalysts at such low temperatures.

MnxCo3−xO4 solid solution as high-efficient catalysts for low-temperature oxidation of formaldehyde

Abstract Mn x Co 3 − x O 4 solid solution was synthesized by co-precipitation method and tested for the first time for oxidation of HCHO. The formation of Mn x Co 3 − x O 4 solid solution was confirmed by XRD, H 2 -TPR, XPS studies. It was observed that complete conversion of HCHO occurred at 75 °C (GHSV = 60,000 h − 1 , relative humidity = 50% (25 °C)), and remained unchanged within 50 h. Such high activity can be ascribed to the large amount of surface oxygen available on Mn x Co 3 − x O 4 . According to the results of in situ DRIFTs, we proposed a reaction pathway for HCHO oxidation over Mn x Co 3 − x O 4 catalyst.

Highly active manganese oxide catalysts for low-temperature oxidation of formaldehyde

Birnessite - type manganese oxides with very high surface areas (up to 154 m 2/g) were successfully prepared using a microemulsion process. The morphology, surface area, pore size, and the surface reducibility of these materials were readily tailored via the synthesis temperature. The physiochemical properties of the manganese oxides were characterized by means of XRD, TEM, SEM, BET and H 2-TPR techniques. These materials were also catalytically tested in HCHO oxidation, showing significantly high catalytic activity. It was found that the differences in catalytic performance of these materials were jointly attributed to the effects of the morphology, surface area and surface reducibility. The highly porous feature of the catalyst with nanospheres could allow HCHO molecules to easily diffuse onto catalytically active sites, which endows the nanospheres with high catalytic activity. The higher the surface area, the higher its catalytic activity. A higher surface reducibility offered a lower temperature of HCHO oxidation. The most active manganese catalyst (BSW-120) showed a 100% HCHO conversion at 100 °C.

High surface area Au/CeO2 catalysts for low temperature formaldehyde oxidation

Gold catalysts supported on high surface area CeO2 were synthesized and tested for low temperature formaldehyde oxidation. It was found that the reactivity was greatly enhanced by increasing surface area of the support. Complete conversion of formaldehyde was obtained on a 3.0Au/CeO2-270 catalyst with a surface area of 270m2g−1 at 50°C, and a conversion of 92.3% was obtained at 37°C over the same catalyst, which made it promising for indoor formaldehyde removal. Detailed characterizations of the catalyst showed that the enhancement could be attributed to two factors. One was that Au species mainly in high oxidation states formed on the high surface area CeO2 resulted in a high degree of HCHO adsorption, as revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy. The other was the high surface area CeO2 provided more oxygen vacancies by the nano effect and the formation of AuxCe1−xO2−δ solid solution as revealed by Raman spectroscopy, on which oxygen molecules could be transformed to active species for the reaction.