Catalysts For HCHO Oxidation Research Articles

The Catalytic and Adsorptive Synergistic Effect of Oxygen-Vacancy-Rich MnOx/C Catalysts for HCHO Oxidation at Room Temperature

The Catalytic and Adsorptive Synergistic Effect of Oxygen-Vacancy-Rich MnO_<i>x</i>/C Catalysts for HCHO Oxidation at Room Temperature

Single-Atom Cationic Ag and Metallic Ag Nanoparticles Supported on Al2O3 as Catalysts for Water-Resistant and CO2-Selective HCHO Oxidation

Ag-based catalysts have been extensively investigated in HCHO oxidation on account of the low price of the Ag precursor and their considerable low-temperature activity. It is known that H2 pretreatment has a remarkable promotion effect on Pt- and Pd- catalysts for HCHO oxidation, whereas the effect of H2 reduction on Ag-based catalysts has been rarely reported, probably due to the coexistence of multiple states of Ag species resulting from the high Ag loading. Herein, we prepared a 1% Ag/Al2O3 (Ag/Al-fresh) catalyst with Ag species in a uniform state and then reduced Ag/Al-fresh with H2 at 600 °C to obtain the Ag/Al-600H2 catalyst. We observed that H2 reduction had a significant influence on the performance of Ag/Al2O3 nanocatalysts in HCHO oxidation. In a dry reaction atmosphere, Ag/Al-fresh and Ag/Al-600H2 exhibited comparable HCHO conversion levels, but Ag/Al-600H2 showed much higher CO2 selectivity than Ag/Al-fresh. The presence of water vapor severely suppressed the HCHO conversion of the Ag/Al-fresh catalyst, while Ag/Al-600H2 showed high water resistance, maintaining high HCHO conversion and CO2 selectivity at 35% RH. Characterization results showed that the Ag species on Ag/Al-fresh and Ag/Al-600H2 were single-atom cationic Ag and metallic Ag nanoparticles, respectively. It was revealed that the Ag0 nanoparticles were more conducive than single-atom Ag+ to formate decomposition, as well as O2 and H2O activation, thus accelerating the conversion of HCOO– and CO intermediates to CO2 and contributing to the higher activity and water resistance of the Ag/Al-600H2 catalyst.

Abnormal inhibiting effect of H2O on Pd/SiO2 and Na–Pd/SiO2 catalysts for HCHO oxidation

Unlike most of Pd-based catalysts, H2O will inhibit the activity of Pd/SiO2 and even Na–Pd/SiO2 catalysts for HCHO oxidation. However, addition of Na significantly improved the regeneration ability of the catalyst.

Acid-Modified Sepiolite-Supported Pt (Noble Metal) Catalysts for HCHO Oxidation at Ambient Temperature

The critical need to enhance the quality of indoor air leads to the improvement of catalyst activity for the removal of formaldehyde. Sepiolite can be utilized in catalytic reactions for its unique structure, composition and high surface area. The adhesion between sepiolite fibers and the blocked microporous channel (by impurities) demands the activation of natural sepiolite through acid treatment. This treatment successfully produces acid-modified sepiolite Pt-supported samples. The impacts of different acid concentrations, Pt loading content and calcination temperature on catalytic activity for formaldehyde (HCHO) oxidation are studied. The catalytic activity of HCHO is characterized and evaluated by techniques including specific surface area, X-ray diffraction, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy and transmission electron microscopy. The results show the maximum specific area of sepiolite at the optimized 0.06 M acid concentration. Among all the prepared samples, the 0.02Pt/Sep catalyst calcined at 500 °C exhibits the highest catalytic activity for the oxidation of HCHO.

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.

Remarkable performance of atomically dispersed cobalt catalyst for catalytic removal of indoor formaldehyde

The single atom catalysts have been widely studied in the catalytic reaction due to their 100% atomic utilization and ultra-high catalytic activity. However, the catalytic removal of formaldehyde on single atom catalysts have not been studied extensively and its catalytic mechanism is still unclear. In this work, atomically dispersed Co catalysts anchored in porous nitrogen-doped carbon were synthetized and the coordination environment of single Co atoms were further proved by the results of XAFS spectrum. The optimal atomically dispersed Co catalysts preformed outstanding removal performance for low-concentration HCHO (∼1 ppm) at room temperature. Furthermore, DFT calculations reveal the HCHO removal mechanism on atomically dispersed Co catalysts, which showed that HCHO molecules can react with O2 molecules adsorbed on single-atom Co sites through the Langmuir-Hinshelwood (L-H) pathway to generate CO2 and H2O at room temperature (HCHO → HCOO* → CO2). This work provides a promising lead for exploring single-atom Co catalysts for HCHO oxidation.

Hydroxyl Groups Promoted Ag Dispersion and Excellent Performance of Ag/Al2O3 Catalyst for HCHO Oxidation

Hydroxyl groups are considered as anchoring sites for active components on catalysts. Guided by this viewpoint, 4 wt. % Ag/Al2O3 catalyst derived from Boehmite (AlOOH) was prepared and showed 100% formaldehyde conversion to CO2 at 75 °C. The results of 1H MAS NMR, UV–vis spectra and Transmission electron microscopy (TEM) images suggest that the abundant bridging OH groups are prominently contributed to Ag anchoring and the formation of large content of small sized metallic Ag with high dispersion and Agnδ+ cluster, and thus facilitating the catalytic oxidation of formaldehyde. This work will pave an attractive way for Ag/Al2O3 catalysts design and application. The enrichment of bridging OH groups of AlOOH contributes to high dispersion of Ag particles and the formation of large content of small sized metallic Ag and Agnδ+ cluster, thus facilitating the HCHO catalytic oxidation.

Sodium-treated sepiolite-supported transition metal (Cu, Fe, Ni, Mn, or Co) catalysts for HCHO oxidation

Sodium-treated sepiolite (NaSep)-supported transition metal catalysts (TM/NaSep; TM = Cu, Fe, Ni, Mn, and Co) were synthesized via a rotary evaporation method. Physicochemical properties of the as-synthesized samples were characterized by means of various techniques, and their catalytic activities for HCHO (0.2%) oxidation were evaluated. Among the samples, Cu/NaSep exhibited superior performance, and complete HCHO conversion was achieved at 100 °C (GHSV = 240000 mL/(g·h)). Additionally, the sample retained good catalytic activity during a 42 h stability test. A number of factors, including elevated acidity, the abundance of oxygen species, and favorable low-temperature reducibility, were responsible for the excellent catalytic activity of Cu/NaSep. According to the results of the in-situ DRIFTS characterization, the HCHO oxidation mechanism was as follows: (i) HCHO was rapidly decomposed into dioxymethylene (DOM) species on the Cu/NaSep surface; (ii) DOM was then immediately converted to formate species; (iii) the resultant formate species were further oxidized to carbonates; (iv) the carbonate species were eventually converted to CO2 and H2O.

Interface effect of mixed phase Pt/ZrO2 catalysts for HCHO oxidation at ambient temperature

High-efficiency Pt/ZrO2 catalysts with a mixed phase were successfully prepared. The catalysts exhibited high activity and their interfacial structure can change the reaction pathway.

Significant enhancement in activity of Pd/TiO2 catalyst for formaldehyde oxidation by Na addition

Developing an effective material for indoor HCHO elimination at ambient temperature is of great significance. In this work, a series of Pd/TiO2 catalysts with different Na loadings were prepared and tested for their activity in HCHO oxidation. The results indicated that Na addition had a remarkable promotion effect on Pd/TiO2 catalysts for HCHO oxidation, and the optimal Na loading was 2wt.%. Features of the catalysts including the reducibility, Pd dispersion and valence state of Pd and O were elucidated using a variety of characterization techniques. The results showed that 2.0Na-Pd/TiO2 exhibited more exposure of active Pd sites and contained abundant surface OH groups, giving it the best HCHO catalytic oxidation performance of the studied catalysts. The 2.0Na-Pd/TiO2 catalyst also had high resistance to effects of space velocity and relative humidity (RH), maintaining high HCHO conversion over a wide gas hourly space velocity range of 80,000–190,000h−1 and RH of 25%–65%.

Fabrication and Performance of Noble Metal Promoted Birnessite Catalysts for Complete Oxidation of Formaldehyde at Low Temperatures.

Noble metal (Au, Ag, Pd and Pt) promoted birnessite (Bir) catalysts were successfully prepared and tested for catalytic oxidation of formaldehyde (HCHO). The catalysts were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), hydrogen temperature programmed reduction (H2-TPR), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and N2 adsorption-desorption. The activities of noble metal (Au, Ag, Pd and Pt) promoted birnessite catalysts follow the order of 1.0Pt/Bir > 1.0Pd/Bir > Bir > 1.0Ag/Bir > 1.0Au/Bir, revealing that the loading of Pd and Pt improves the catalytic activity of birnessite, but the loading of Ag and Au slightly decreases the catalytic activity of birnessite. Effects of the Pt loading amount were also investigated on the activity of Pt/Bir catalysts for HCHO oxidation. Pt/Bir with a Pt loading of 1.5 wt% (1.5 Pt/Bir), which has the best reduction properties, was found to be the most efficient catalyst. Over this catalyst, HCHO could be completely oxidized into CO2 and H2O at 70°. 1.5 Pt/Bir also shows good catalytic stability under the HCHO oxidation atmosphere. The differences in the catalytic activity of these materials are largely attributed to their reducibility as well as the dispersion of metal nanoparticles, but are not directly related to their specific surface areas.

Catalytic removal of formaldehyde at room temperature over supported gold catalysts

Two kinds of Au/CeO2, prepared by deposition–precipitation (DP) using urea (U) or NaOH (N) as precipitants were investigated as catalysts for HCHO oxidation. H2-TPR and XPS techniques were used to characterize the Au/CeO2 samples. Due to the generation of increased amounts of active surface oxygen species resulting from the strong Au–CeO2 interaction, the Au/CeO2 (DPU) catalyst showed higher activity than the DPN catalyst, achieving 100% conversion of HCHO into CO2 and H2O at room temperature, even in the presence of water and at high GHSV (143,000h−1); moreover, the conversion was stable for at least 60h. The reaction mechanism and the rate limiting steps for HCHO oxidation over the Au/CeO2 catalysts were identified by means of in situ DRIFTS studies. The influence of oxygen and water on the formation and consumption of the formate reaction intermediates was also investigated. Results suggest that Au/CeO2 (DPU) is a promising catalyst for HCHO removal under real world conditions.