Room-temperature Catalytic Oxidation Research Articles

Efficient and Durable Oxidation Removal of Formaldehyde over Layered Double Hydroxide Catalysts at Room Temperature.

Room temperature catalytic oxidation (RTCO) using non-noble metals has emerged as a highly promising technique for removal of formaldehyde (HCHO) under ambient conditions; however, non-noble catalysts still face the challenges related to poor water resistance and low stability under harsh conditions. In this study, we synthesized a series of layered double hydroxides (LDHs) incorporating various dual metals (MgAl, ZnAl, NiAl, NiFe, and NiTi) for formaldehyde oxidation at ambient temperature. Among the synthesized catalysts, the NiTi-LDH catalyst showed an HCHO removal efficiency and CO2 yield close to 100.0%, and exceptional water resistance and chemical stability on running 1300 min. The abundant hydroxyl groups in LDHs directly bonded with HCHO, leading to the production of CO2 and H2O, thus inhibiting the formation of CO, even in the absence of O2 and H2O. The coexistence of O2 effectively reduced the reaction barrier for H2O molecule dissociation, facilitating the formation of hydroxyl groups and their subsequent backfill on the catalyst surface. The mechanisms underlying the involvement and regeneration of hydroxyl groups in room temperature oxidation of formaldehyde were elucidated with the combined in situ DRIFTS, HCHO-TPD-MS, and DFT calculations. This work not only demonstrates the potential of LDH catalysts in environmental applications but also advances the understanding of the fundamental processes involved in room temperature oxidation of formaldehyde.

Highly Dispersed Ni Atoms and O3 Promote Room-Temperature Catalytic Oxidation.

Transition metal oxides are promising catalysts for catalytic oxidation reactions but are hampered by low room-temperature activities. Such low activities are normally caused by sparse reactive sites and insufficient capacity for molecular oxygen (O2) activation. Here, we present a dual-stimulation strategy to tackle these two issues. Specifically, we import highly dispersed nickel (Ni) atoms onto MnO2 to enrich its oxygen vacancies (reactive sites). Then, we use molecular ozone (O3) with a lower activation energy as an oxidant instead of molecular O2. With such dual stimulations, the constructed O3-Ni/MnO2 catalytic system shows boosted room-temperature activity for toluene oxidation with a toluene conversion of up to 98%, compared with the O3-MnO2 (Ni-free) system with only 50% conversion and the inactive O2-Ni/MnO2 (O3-free) system. This leap realizes efficient room-temperature catalytic oxidation of transition metal oxides, which is constantly pursued but has always been difficult to truly achieve.

Alkali-modified copper manganite spinel for room temperature catalytic oxidation of formaldehyde in air

Formaldehyde (FA) is present ubiquitously in indoor environment as a hazardous pollutant with carcinogenic risks. For the efficient mitigation of FA, catalytic oxidation is a recommendable option to simultaneously satisfy both material cost (e.g., avoiding noble metals) and low-energy requirement (under dark and at room temperature (RT)). From this perspective, a cost-effective alkali modified copper manganite spinel (CuMn2O4) catalyst has firstly been prepared and employed for FA oxidation. Specifically, alkali (1 mol L−1 potassium hydroxide)-modified CuMn2O4 (1-CuMn2O4) achieves 100% FA (50 ppm (gas hourly space velocity of 4777 h−1)) conversion (XFA) at RT. The steady-state reaction rate of 1-CuMn2O4 at 10% XFA is 8.18 × 10−2 mmol g−1 h−1. According to in situ diffuse reflectance infrared Fourier transform spectroscopy, FA molecules are oxidized into water and carbon dioxide through dioxymethylene and formate intermediates. Based on density functional theory simulation, the higher catalytic performance of 1-CuMn2O4 for FA oxidation is attributed to the combined effects of firmer attachment of FA molecules to 1-CuMn2O4 surface, lower energy cost of FA adsorption, and lower desorption energy for the final products from the substrate surface. The present work is expected to provide insights into high-performing non-noble metal catalysts for RT oxidative removal of FA from indoor air.

Room Temperature Catalysts for High Effective Degradation of Formaldehyde: Research Progresses and Challenges

AbstractFormaldehyde (HCHO) is one of major pollutants in indoor air, and prolonged exposure to HCHO may result in great harm to human health. Therefore, it is crucial to remove HCHO from indoor air at room temperature. In recent years, various room temperature catalysts, which have the advantages of environmental friendliness and energy saving, were developed for high effective catalytic oxidation of HCHO. In this work, research progress and challenges on the room temperature catalytic oxidation of HCHO by using noble metal catalysts and non‐noble metal catalysts are systemically reviewed. Meanwhile, the room temperature catalytic oxidation performance, degradation conditions of HCHO, and room temperature catalytic oxidation mechanism of catalysts was also discussed.

Electrospinning synthesis of Co3O4 porous nanofiber monolithic catalysts for the room-temperature indoor catalytic oxidation of formaldehyde at low concentrations

Room-temperature catalytic oxidation is a highly promising method for controlling formaldehyde (HCHO) concentrations indoors because it does not require any additional energy input, while completely converting HCHO into harmless H2O and CO2. This study focuses on the synthesis of Co3O4 porous nanofiber monolithic catalysts through electrospinning and investigates the mechanism behind the formation of its porous structure by analyzing the morphological changes that occur during the calcination of its fibers. In this research, we utilized heat-resistant polyacrylonitrile (PAN) as template to synthesize Co3O4 porous nanofiber monolithic catalysts. The synthesis process involved the utilization of the oxidation characteristics of PAN in the presence of cobalt acetate tetrahydrate (CH3COO)2Co·4H2O at 270–330 °C. Co3O4 porous nanofiber monolithic catalyst demonstrated exceptional performance, exhibiting over 99% catalytic activity toward HCHO at room-temperature in indoors (10–12 ppm, 25 °C) at a gas hourly space velocity of 60,000 mL·g−1h−1. This catalyst demonstrates its suitability for practical applications and its potential for energy savings. These results highlight the superiority of Co3O4 porous nanofiber monolithic catalyst over catalysts produced via the direct calcination method. The outstanding activity and stability of Co3O4 porous nanofiber monolithic catalyst make it a promising candidate for applications requiring efficient formaldehyde removal, particularly in indoors.

Zn-doped MnCe catalyst designed and applied for indoor low concentration formaldehyde removal and simultaneous antibacterial

As typical indoor air pollutants, the simultaneous removal of formaldehyde and microorganisms at room temperature was significant to purify indoor environment satisfactorily. Based on the practical problems of room temperature catalytic oxidation, Zn-doped MnCe (MC-Zn) aerogel catalysts were designed with dual functions of catalytic oxidation and bacterial inhibition in this study. It was found that MC aerogel exhibited excellent formaldehyde removal performance, which obtained 97.6% formaldehyde removal efficiency at 24 h. Besides, a small amount of Zn doping had little effect on the Lewis acidic sites and Mn3+/Mn on the MC aerogel catalyst surface, and the equivalent formaldehyde removal efficiency was achieved with the increasing specific surface area.The antibacterial tests demonstrated that the Zn-doped catalysts inhibited the growth of Staphylococcus aureus(S. aureus), Bacillus subtilis(B. subtilis) and Escherichia coli(E. coli). When the molar ratio of Mn:Zn:Ce was 5:1:4, the catalyst exhibited the optimal room temperature catalytic oxidation activity and appropriate bacterial inhibition performance. This paper provides a technical reference for the effective treatment of indoor co-contaminated environment.

Synergetic modulation of molecular oxygen activation and surface acidity/basicity on defective M/UiO-66m (M = Pt, Pd) for advanced oxidation of gaseous formaldehyde at room temperature

Molecular oxygen (O2) dominated room temperature catalytic oxidation (RTCO) technique is essential for removing indoor formaldehyde (HCHO) and guaranteeing indoor air safety. However, RTCO is challenged by low O2 activation efficiency and uncontrollable O2 activation pathway. In this study, defective UiO-66 (UiO-66m) with abundant coordinatively unsaturated Zr-sites (Zr-CUSs) is exploited for anchoring well-dispersed noble metals (M = Pt, Pd) and tuning surface acidity/basicity. The strong interfacial electronic metal support interactions at Zr-CUSs–M active centers trigger O2 activation into mobile ROS (superoxide radicals (•O2−), singlet oxygen (1O2)) at room temperature. Consequently, adsorbed HCHO can be efficiently oxidized into CO2 with exceptional mineralization efficiency (over 90%) and considerable recyclability (6 runs, 6 h). A novel ROS-initiated advanced oxidation pathway, together with the synergetic acid/base catalytic effects, is proposed based on in situ spectroscopic studies. This study will provide new insights into the O2 activation pathway and designing advanced RTCO catalysts.

Design and Synthesis of Amphiphilic Catalyst [C16mim]5VW12O40Br and Its Application in Deep Desulfurization with Superior Cyclability at Room Temperature.

Achieving long-term stable deep desulfurization at room temperature and recovering high value-added sulfone products is a challenge at present. Herein, a series of catalysts [Cnmim]5VW12O40Br (CnVW12, 1-alkyl-3-methylimidazolium bromide tungstovanadate, n = 4, 8, 16) were presented for the room temperature catalytic oxidation of dibenzothiophene (DBT) and its derivatives. Factors affecting the reaction process, such as the amount of catalyst, oxidant, and temperature, were systematically discussed. C16VW12 showed higher catalytic performance, and 100% conversion and selectivity could be achieved in 50 min with only 10 mg. The mechanism study showed that the hydroxyl radical was the active radical in the reaction. Benefiting from the "polarity strategy", the sulfone product accumulated after 23 cycles in a C16VW12 system, and the yield and purity were about 84% and 100%, respectively.

Hierarchical Pt/NiCo2O4 nanosheets decorated carbon nanofibers for room-temperature catalytic formaldehyde oxidation

Room-temperature catalytic formaldehyde (HCHO) oxidation is regarded as the most promising way for constant and oxidative removal of indoor HCHO. Herein, carbon nanofibers (CNF) with three-dimensional (3D) interconnection network structure decorated with Pt/NiCo2O4 alloy nanosheets (Pt/NiCo2O4/CNF) were fabricated in-situ to catalyze the oxidation of HCHO at ambient temperature. The presence of CNF helps to inhibit the aggregation of NiCo2O4 nanosheets, expose more active sites and form a hierarchically porous structure, which is conducive to the dispersion of platinum nanoparticles (NPs) and the diffusion of reactants. Besides, oxygen vacancies from Pt-loading process ensure abundant active oxygen species, which are beneficial to HCHO oxidation. Moreover, CNF with microporous structure can strongly adsorb HCHO, rapidly reduce the concentration of HCHO in air and increase its concentration near Pt/NiCo2O4, thus accelerating the formaldehyde oxidation reaction. At Pt content as low as 0.5 wt%, Pt/NiCo2O4/CNF exhibits superior HCHO oxidation activity, and conversion of 92.4% can be achieved within 60 min due to the combination of adsorption and oxidation. This work may shed light on fabricating CNF-based 3D catalysts for the practical application of indoor HCHO elimination.

Large-scale facile green synthesis of porous silver nanocubes on monolithic activated carbon for room-temperature catalytic oxidation of formaldehyde

Large-scale facile green synthesis of porous silver nanocubes on monolithic activated carbon for room-temperature catalytic oxidation of formaldehyde

MnCo-Layered double hydroxides nanosheets supported Pd nanoparticles for complete catalytic oxidation of formaldehyde at room temperature

Removal of gaseous formaldehyde by room-temperature catalytic oxidation has promising applications. The rational design of the structure of catalyst to improve the ability of activated key species (adsorbed oxygen and hydroxyl) through understanding the reaction mechanism can improve the catalytic activity. In this paper, Pd nanoparticles were deposited on pre-reduction uniform LDH nanosheets to prepare Pd-decorated sodium borohydride-reduced Mn/Co layered double hydroxides (Pd/LDH-NaBH4). The transition metal (Mn and Co) doping of Pd improved the catalyst's ability to activate oxygen and formaldehyde, and the support of LDHs increased the hydroxyl concentration of the catalyst. Pd/LDH-NaBH4 showed reduced valence of Pd, improved dispersion of Pd NPs, and retention of abundant hydroxyl groups on LDH. Characterizations revealed that the synergistic effect of the supported Pd NPs and LDH, as well as many oxygen vacancies, was responsible for the effective removal of HCHO by Pd/LDH-NaBH4 catalyst at ambient temperature. This study further developed a new catalyst for HCHO oxidation, which may provide a new idea for the removal mechanism of oxidized HCHO.

One-step fabrication of Pd-embedded hierarchically porous carbon micro-spheres for formaldehyde removal under mild conditions

Using the enclosed space of Pickering emulsion droplets as a template, we adopted a one-step strategy to prepare Pd and N co-doped multi-core layered porous carbon microspheres (Pd@NCMs-T) for room-temperature catalytic oxidation of HCHO.

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.

Three-dimensional carbon foam supported MnO2/Pt for rapid capture and catalytic oxidation of formaldehyde at room temperature

Catalytic oxidation of formaldehyde (HCHO) at room temperature is one of the most viable approaches to indoor HCHO pollution abatement. Herein, three-dimensional (3D) carbon foam decorated with Pt/MnO2 nanosheets (Pt/MnO2-CF) was in-situ synthesized for room-temperature catalytic oxidation of HCHO. The 3D Pt/MnO2-CF with a low platinum content of 0.3 wt% exhibited excellent catalytic activity because of its hierarchically porous structure facilitating the diffusion of reactant molecules. Moreover, an abundance of active oxygen species resulting from oxygen vacancies are favorable for HCHO oxidation. In addition, the carbon foam substrate exhibited a very good HCHO adsorption capability, which helps achieve prompt reduction in HCHO concentration in the gas-phase and subsequent complete oxidation of adsorbed HCHO. The combination of adsorption and oxidation was more favorable for oxidative decomposition of HCHO. This work demonstrates that such 3D nanocomposites with low noble metal loading have promising application for indoor HCHO removal and air purification.

Room-temperature formaldehyde catalytic decomposition

The necessity, basic strategies and mechanisms for HCHO room-temperature catalytic oxidation removal are summarized and discussed.

Probing the room-temperature oxidative desulfurization activity of three-dimensional alkaline graphene aerogel

Room-temperature catalytic oxidation of H2S has emerged as an intriguing solution to the H2S elimination, but is currently challenged by desulfurizers’ low capacity. Herein, three-dimensional alkaline graphene aerogels are prepared and demonstrated to be highly efficient catalysts for H2S oxidation, achieving 3.19 g/g of breakthrough capacity. Such high sulfur capacity is attributed to the interconnected graphene network consisting of graphene sheets, providing more product storehouse compared with traditional porous carbons. Further, a radical-induced reaction pathway of H2S oxidation is proposed that oxygen molecules could be activated to form superoxide radicals merely on graphene, which induces the dissociated HS− oxidation to sulfur. The characterization results also uncover that the formed sulfur goes through a process of nucleation and growth on graphene sheets. The current work could provide critical insights into the behavior of H2S oxidation and therefore offers a novel route of developing catalysts with large sulfur capacity at room temperature.

In Situ Intermediates Determination and Cytotoxicological Assessment in Catalytic Oxidation of Formaldehyde: Implications for Catalyst Design and Selectivity Enhancement under Ambient Conditions.

Formation and decay of formaldehyde oxides (CH2OO) affect the complete oxidation of formaldehyde. However, the speciation and reactivity of CH2OO are poorly understood because of its extremely fast kinetics and indirect measurements. Herein, three isomers of CH2OO (i.e., main formic acid, small dioxirane, and minor CH2OO Criegee) were in situ determined and confirmed as primary intermediates of the room-temperature catalytic oxidation of formaldehyde with two reference catalysts, that is, TiO2/MnO x-CeO2 and Pt/MnO x-CeO2. CH2OO Criegee is quite reactive, whereas formic acid and dioxirane have longer lifetimes. The production, stabilization, and removal of the three intermediates are preferentially performed at high humidity, matching well with the decay rate of CH2OO at approximately 6.6 × 103 s-1 in humid feed gas faster than 4.0 × 103 s-1 in dry feed. By contrast, given that a thinner water/TiO2 interface was well-defined in TiO2/MnO x-CeO2, fewer reductions in the active sites and catalytic activity were found when humidity was decreased. Furthermore, lethal intermediates mostly captured at the TiO2/MnO x-CeO2 surface suppressed the toxic off-gas emissions. This study provides practical insights into the rational design and selectivity enhancement of a reliable catalytic process for indoor air purification under unfavorable ambient conditions.

Insight into room-temperature catalytic oxidation of NO by CrO2(110): A DFT study

The NO oxidation processes on CrO2(110) was investigated by virtue of DFT + U calculation together with microkinetic analysis, aiming to uncover the reaction mechanism and activity-limiting factors for CrO2 catalyst. It was found that NO oxidation on CrO2(110) has to be triggered with the lattice Obri involved (Mars-van Krevelen mechanism) rather than the Langmuir-Hinshelwood path occurring at the Cr5c sites alone. Specifically, the optimal reaction path was identified. Quantitatively, the microkinetic analysis showed that CrO2(110) can exhibit a high turnover rate of 0.978 s-1 for NO oxidation at room temperature. Such an activity could originate from the bifunctional synergetic catalytic mechanism, in which the Cr5c sites can exclusively adsorb NO and the Obri is very reactive and provides oxidative species. However, it is worth noting that, as the reactive Obri tightly binds NO2, the nitrate species was found to be difficult removed and constituted the key poisoning species, eventually limiting the overall activity of CrO2. This work demonstrated the considerable catalytic ability of CrO2 for NO oxidation at room temperature, and the understanding may facilitate the further design of more active Cr-based catalyst.

Insight into Room-Temperature Catalytic Oxidation of Nitric oxide by Cr2O3: A DFT Study

Cr-based catalysts have drawn attention as promising room-temperature NO oxidation catalysts. However, the intrinsic active component and reaction mechanism at the atomic level remain unclear. Here, taking the Cr2O3, one of the most stable chromium oxides, as an object, we systematically investigated NO oxidation processes on Cr2O3(001) and -(012) surfaces by virtue of DFT+U calculations, aiming to uncover the activity-limiting factors and basic structure–activity relationship of the Cr2O3 catalyst. It was revealed that NO oxidation could not proceed via a Mars–van Krevelen mechanism involving the lattice oxygen on both surfaces. For the Cr2O3(001) surface exposing the isolated three-coordinated Cr3c, the reactions are inclined to occur through the Eley–Rideal route, in which the NO couples directly with the molecular O2* or atomic O* adsorbed at the Cr3c site to form two key intermediate species (ONOO* and NO2*) following a barrierless process. Nevertheless, the overall activity is limited by the irrever...

A General Silica-Templating Synthesis of Alkaline Mesoporous Carbon Catalysts for Highly Efficient H2S Oxidation at Room Temperature.

A general synthesis of alkaline mesoporous carbons (AMCs) is developed based on a simplified silica-templating method for room-temperature catalytic oxidation of H2S. The key to the success relies on dissolving the silica templates to create the interconnected mesoporous structure as well as leaving parts of the alkaline products in the pores; both of them are prerequisites for H2S oxidation. By adjusting the alkaline etching degree and organic/inorganic ratio, the porosity and basicity of the AMC could be simultaneously tuned, allowing the AMCs direct use for H2S catalytic oxidation with an unprecedented removal capacities of 4.49 ± 0.12 g/g. Such excellent catalytic performance should be attributed to the developed pore structure that stores the product sulfur and the strong basicity that promotes the dissociation of H2S into HS- ions. Moreover, this simplified silica-templating method could be easily extended to the preparation of various silica templated mesoporous carbon catalysts. All these AMCs demonstrate a successful combination of low cost with high performance, which may well be the answer for the technical development of industrial H2S removal.