Influence of pretreatment on the catalytic performance of Ag/CeO2 for formaldehyde removal at low temperature

A robust, eco-friendly, and biodegradable cellulose nanofiber composite film for highly effective formaldehyde removal at room temperature

Formaldehyde (HCHO) poses a significant threat as a common indoor air pollutant, leading to various health issues. However, effectively addressing HCHO removal at room temperature remains a considerable challenge. This paper presents the preparation of a robust, eco-friendly, and biodegradable composite cellulose nanofiber film, incorporating CeO2-Ag@MnO2 catalysts and TEMPO-oxidized cellulose nanofiber (TOCNF), for high-efficiency HCHO removal at room temperature. A CeO2-Ag@MnO2 ternary catalyst with a core-shell structure was constructed to enhance the catalytic oxidation activity and stability. This structure increased the number of active sites on the catalyst surface and enhanced the interfacial synergistic effect of Ce-Ag-Mn. The TOCNF physically adsorbed HCHO in the composite film, while the catalyst oxidized it to CO2 and water. The composite films, particularly those with 20 wt% CeO2-Ag@MnO2 catalyst, exhibited high HCHO removal rates of 91.2 % at 20 °C and 99.6 % at 60 °C. Furthermore, the TOCNF/20 CAM composite films demonstrated excellent mechanical properties and degradability. This composite film offers an efficient and eco-friendly solution for the catalytic oxidation of HCHO at room temperature.

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.

Low-temperature oxidative removal of gaseous formaldehyde by an eggshell waste supported silver-manganese dioxide bimetallic catalyst with ultralow noble metal content

Under dark/low temperature (DLT) conditions, the oxidative removal of gaseous formaldehyde (FA) was studied using eggshell waste supported silver (Ag)-manganese dioxide (MnO₂) bimetallic catalysts. To assess the synergistic effects between the two different metals, 0.03%-Ag-(0.5-5%)-MnO₂/Eggshell catalysts were prepared and employed for DLT-oxidation of FA. The steady-state FA oxidation reaction rate (mmol g^-1 h^-1), when measured using 100 ppm FA at 80 °C (gas hourly space velocity (GHSV) of 5308 h^-1), varied as follows: Ag-1.5%-MnO₂/Eggshell-R (9.4) > Ag-3%-MnO₂/Eggshell-R (8.1) > Ag-1.5%-MnO₂/Eggshell (7.5) > Ag-5%-MnO₂/Eggshell-R (7.2) > Ag-1.5%-MnO₂/CaCO₃-R (6.8) > MnO₂-R (6) > Ag-0.5%-MnO₂/Eggshell-R (3.2) > Ag/Eggshell-R (2.6). (Here, 'R' denotes hydrogen-based thermochemical reduction pretreatment.) The temperature required for 90% FA conversion (T₉₀) at the same GHSV exhibited a contrary ordering: Ag/Eggshell-R (175 °C) > Ag-0.5%-MnO₂/Eggshell-R (123 °C) > Ag-5%-MnO₂/Eggshell-R (113 °C) > MnO₂-R (99 °C) > Ag-1.5%-MnO₂/Eggshell (96 °C) > Ag-3%-MnO₂/Eggshell-R (93 °C) > Ag-1.5%-MnO₂/Eggshell-R (77 °C). The eggshell catalyst outperformed the ones made of commercial calcium carbonate due to the presence of defects in the former. The MnO₂ co-catalyst enhances the catalytic activities through the capture and activation of atmospheric oxygen (O₂) with rapid catalytic regeneration. Also, MnO₂ favorably captures the hydrogen of the adsorbed FA molecules to make the oxidation pathway thermodynamically more favorable.

Bifunctional zeolites-silver catalyst enabled tandem oxidation of formaldehyde at low temperatures

Bifunctional catalysts with tandem processes have achieved great success in a wide range of important catalytic processes, however, this concept has hardly been applied in the elimination of volatile organic compounds. Herein, we designed a tandem bifunctional Zeolites-Silver catalyst that enormously boosted formaldehyde oxidation at low temperatures, and formaldehyde conversion increased by 50 times (100% versus 2%) at 70 °C compared to that of monofunctional supported silver catalyst. This is enabled by designing a bifunctional catalyst composed of acidic ZSM-5 zeolite and silver component, which provides two types of active sites with complementary functions. Detached acidic ZSM-5 activates formaldehyde to generate gaseous intermediates of methyl formate, which is more easily oxidized by subsequent silver component. We anticipate that the findings here will open up a new avenue for the development of formaldehyde oxidation technologies, and also provide guidance for designing efficient catalysts in a series of oxidation reactions.

Degradation of Formaldehyde over MnO2/CeO2 Hollow Spheres: Elucidating the Influence of Carbon Sphere Self-Sacrificing Templates

Here, we prepare a MnO₂/CeO₂ hollow sphere catalyst using the carbon sphere as a self-sacrificing template for formaldehyde (HCHO) removal. In the feed gas of 20 ppm of HCHO (balanced by N₂) + 20 vol % O₂, a HCHO removal efficiency of 70% was achieved at 20 °C and full conversion was reached at around 47 °C at GHSV = 50,000 mL (g_cat h)^-1 for MnO₂/CeO₂ hollow spheres. The catalytic performance and structural and chemical properties of MnO₂/CeO₂ hollow spheres for the removal of core carbon spheres were explored, and the influence of using the carbon sphere as a self-sacrificing template was proved by comparing with carbon@MnO₂/CeO₂ (a core carbon sphere with a MnO₂/CeO₂ shell) and nonmorphologic MnO₂/CeO₂. The properties of the MnO₂/CeO₂ hollow spheres are significantly improved compared to carbon@MnO₂/CeO₂ (removal efficiency of 45% at 150 °C) and MnO₂/CeO₂ (removal efficiency of 46% at 20 °C) as a result of an evolution in the interaction between Mn/Ce and carbon. This increase in the interaction strength seems to (i) increase the oxygen vacancy, (ii) promote the oxygen species mobility, and (iii) improve the chemical stability of the MnO₂/CeO₂ hollow spheres. We believe that these results are beneficial to the fabrication of binary transition metal oxides and applications of them in HCHO removal.