Synergically regulated silver species and surface oxygen on manganese oxide for promoted activity of formaldehyde oxidation

Formaldehyde (HCHO) is a common indoor pollutant that is detrimental to human health. Its efficient removal has become an urgent demand to reduce the public health risk. In this work, Ag-MnOx-based catalysts were prepared and activated under different atmosphere (i.e., air, hydrogen (H2) and carbon monoxide (CO)) for efficient oxidation of HCHO. The catalyst activated with CO (Ag/Mn-CO) displayed the highest activity among the tested samples with 90% conversion at 100°C under a gas space velocity of 75,000 mL/(gcat·hr). Complementary characterizations demonstrate that CO reduction treatment resulted in synergically regulated content of surface oxygen on support to adsorb/activate HCHO and size of Ag particle to dissociate oxygen to oxidize the adsorbed HCHO. In contrast, other catalysts lack for either abundant surface oxygen species or metallic silver with the appropriate particle size, so that the integrate activity is limited by one specific reaction step. This study contributes to elucidating the mechanisms regulating the oxidation activity of Ag-based catalysts.

Synergistic effect of photo-thermal oxidation for a low concentration of HCHO over Bi3+-TiO2/MnFeOx catalysts at ambient temperature

Formaldehyde (HCHO) has been one of the important air pollutants, and the effective removal of HCHO at ambient temperature has been a big challenge. In this work, the synergistic effect of photo-thermal oxidation with Bi³⁺-TiO₂/MnFeO_x for a low concentration of HCHO was investigated. MnFeO_x was synthesized by the complexation method (CM) and co-precipitation (CP), and TiO₂ with Bi³⁺ doping supported on MnFeO_x was prepared by using the hydrothermal method to obtain a higher oxidation performance. The results demonstrated an excellent oxidation activity of MnFeO_x (CM) for HCHO at ambient temperature, attributed to the morphology effect (large surface areas and small crystal sizes), the large absorption of oxygen, and the interaction and oxygen vacancy formed between MnO₂ and FeO_x. Although Bi³⁺-TiO₂/MnFeO_x showed a similar result as MnFeO_x at 48 h, the oxidation activities for HCHO were improved prominently under photo-thermal oxidation at 12 h. The improvement was ascribed to the synergistic effect of Bi³⁺-TiO₂ and MnFeO_x with surface adsorbed oxygen, and more generated reactive oxygen species on the surface. In particular, 2 wt% Bi³⁺-TiO₂/MnFeO_x displayed the highest activity (90.2%) and good stability (5 cycles), and the HCHO average conversion was increased from 46.2 to 58.2% at 12 h. The feasible oxidation mechanism and reaction pathway were also interpreted. This work provides a new insight for the development of photocatalysts supported on transition metal oxides to oxidize HCHO at ambient temperature.

High-Performance Indium–Tin Oxide (ITO) Electrode Enabled by a Counteranion-Free Metal–Polymer Complex

Although multicomponent inorganic thin films (metal-oxides, -carbides, -nitrides, and -chalcogenides) have been synthesized by polymer-assisted deposition (PAD), synthesis of high-performance transparent conducting oxides (TCOs) has been rarely reported. TCO requires (i) removal of impurities, (ii) high-density oxide film, (iii) homogeneity in crystal structures and film morphology, and (iv) controllable elemental doping. This study performs a systematic investigation on preparation of stable multicomponent metal-polymer complex solutions by removing the counteranions in the solution. This study also proposes accurate acid-base titration for each metal species in order to minimize the amount of PEI, thus maximizing the density of the film. As a representative TCO, Sn-doped In₂O₃ (ITO) films have been achieved. The ITO film has an excellent sheet resistance (24.5 Ω/sq) at 93% optical transparency, with a figure of merit of 2.1 × 10^-2 Ω^-1, which is comparable to the best.

Low-Temperature Selective Catalytic Reduction of NO x with NH3 over Mn-Ce Composites Synthesized by Polymer-Assisted Deposition

The Mn _x Ce _y binary catalysts with a three-dimensional network structure were successfully prepared via a polymer-assisted deposition method using ethylenediaminetetraacetic acid and polyethyleneimine as complexing agents. The developed pore structure could facilitate the gas diffusion and accelerate the catalytic reaction for NH₃ selective catalytic reduction (SCR). Moreover, the addition of Ce is beneficial for the exposure of active sites on the catalyst surface and increases the adsorption of the NH₃ and NO species. Therefore, the Mn₁Ce₁ catalyst exhibits the best catalytic activity for NO _x removal with a conversion rate of 97% at 180 °C, superior water resistance, and favorable stability. The SCR reaction over the Mn₁Ce₁ catalyst takes place through the E-R pathway, which is confirmed by the in situ diffuse reflectance Fourier transform analysis. This work explores a new strategy to fabricate multimetal catalysts and optimize the structure of catalysts.

The Catalytic Oxidation of Formaldehyde by FeOx-MnO2-CeO2 Catalyst: Effect of Iron Modification

A series of FeOx-MnO2-CeO2 catalysts were synthesized by the surfactant-templated coprecipitation method and applied for HCHO removal. The influence of Fe/Mn/Ce molar ratio on the catalytic performance was investigated, and the FeOx-MnO2-CeO2 catalyst exhibited excellent catalytic activity, with complete HCHO conversion at low temperatures (40 °C) when the molar ratio of Fe/Mn/Ce was 2/5/5. The catalysts were characterized by N2 adsorption and desorption, XRD, H2-TPR, O2-TPD and XPS techniques to illustrate their structure–activity relationships. The result revealed that the introduction of FeOx into MnO2-CeO2 formed a strong interaction between FeOx-MnO2-CeO2, which facilitated the improved dispersion of MnO2-CeO2, subsequently increasing the surface area and aiding pore development. This promotion effect of Fe enhanced the reducibility and produced abundant surface-active oxygen. In addition, a great number of Oα is beneficial to the intermediate decomposition, whereas the existence of Ce3+ favors the formation of oxygen vacancies on the surface of the catalyst, all of which contributed to HCHO oxidation at low temperatures.

Catalytic Oxidation of HCHO over the Sodium-Treated Sepiolite-Supported Rare Earth (La, Eu, Dy, and Tm) Oxide Catalysts

The sodium-treated sepiolite (NaSep)-supported rare earth oxide (RE/NaSep; RE = La, Eu, Dy, and Tm) samples were prepared using the rotary evaporation method. Physicochemical properties of these materials were characterized by XRD, SEM, BET, FTIR, XPS, H2–TPR, NH3–TPD, and in situ DRIFTS, and their catalytic activities for formaldehyde (HCHO) (2000 ppm) oxidation were evaluated. The results show that loading of the rare earth oxide on NaSep improved its catalytic performance. Among all the samples, Eu/NaSep performed the best, and complete HCHO conversion was achieved at a temperature of 150 °C and a gas hourly space velocity of 240,000 mL/(g h); a good catalytic activity was still maintained after 45 h of stability test. The catalytic oxidation mechanism of HCHO was studied using the in situ DRIFTS technique. As a result, the effective and stable catalytic performance of the Eu/NaSep sample was mainly due to the presence of hydroxyl groups on the sepiolite surface and the doped rare earth oxides, which contributed to its high performance. HCHO oxidation underwent via the steps of HCHO + O2 → HCOO− + OH− → H2O + CO2. It is concluded that the optimal catalytic activity of Eu/NaSep was associated with the highest Oads/Olatt atomic ratio, the largest amount of hydroxyl groups, the highest acidity, and the best reducibility. The present work may provide new insights into the application in the removal of high-concentration HCHO over the rare earth oxides supported on natural low-cost clays.

Effect of ceria promotion on the catalytic performance of Ni/SBA-16 catalysts for CO2 methanation

The presence of Ce inside the SBA-16 structure promoted the ratio of Ce³⁺ and medium basic sites and thus favoured CH₄ formation.

Ultra-small CeO2 nanoparticles supported on SiO2 for indoor formaldehyde oxidation at low temperature

Ultra-small CeO₂ nanocrystals with a size of 2.5 nm were synthesized for high efficiency HCHO oxidation at low temperature.