A Pair-Electrosynthesis for Formate at Ultra-Low Voltage Via Coupling of CO_(2) Reduction and Formaldehyde Oxidation

Formate can be synthesized electrochemically by CO_(2) reduction reaction(CO_(2)RR)or formalde-hyde oxidation reaction(FOR).The CO_(2)RR approach suffers from kinetic-sluggish oxygen evolution reac-tion at the anode.To this end,an electrochemical sys-tem combining cathodic CO_(2)RR with anodic FOR was developed,which enables the formate electrosynthesis at ultra-low voltage.Cathodic CO_(2)RR employing the BiOCl electrode in H-cell exhibited formate Faradaic efficiency(FE)higher than 90% within a wide potential range from−0.48 to−1.32 V_(RHE).In flow cell,the current density of 100 mA cm^(−2) was achieved at−0.67 V_(RHE).The anodic FOR using the Cu_(2)O electrode displayed a low onset potential of−0.13 V_(RHE) and nearly 100%formate and H_(2) selectivity from 0.05 to 0.35 V_(RHE).The CO_(2)RR and FOR were constructed in a flow cell through membrane electrode assembly for the electrosynthesis of formate,where the CO_(2)RR//FOR delivered an enhanced current density of 100 mA cm^(−2) at 0.86 V.This work provides a promising pair-electrosynthesis of value-added chemicals with high FE and low energy consumption.

Ag-Based Catalysts in Different Supports: Activity for Formaldehyde Oxidation

Through the impregnation method, Ag catalysts with different support (such as TiO2 and γ-Al2O3) were prepared and then tested for catalytic oxidation of formaldehyde (HCHO) at low temperatures. The Ag/TiO2 catalyst exhibited strong catalytic performance, converting HCHO to CO2 and H2O at around 95°C. However, the Ag/Al2O3 catalysts showed much lower activity and reached 100% conversion at 125°C. The Ag-based catalysts were next characterized by several methods (XRD, TEM, FT-R, BET and H2-TPR). Results of characterization revealed that support dramatically impacts the size and dispersion of Ag particles. The XRD analysis showed the existence of different peaks of the silver on the surface of Al2O3 in the contrast with TiO2 no specific peaks exist. Therefore, the size of the Ag particles and their dispersion are the most important factors that affect their catalytic performance for formaldehyde oxidation. In terms of catalytic performance for HCHO oxidation, the Ag/TiO2 catalyst possesses the best Ag dispersion, as well as the smallest Ag particle size.

Light-enhanced metal-support interaction for synergetic photo/thermal catalytic formaldehyde oxidation

The strong metal-support interaction(SMSI)plays a pivotal role in regulating electronic properties and activating surface oxygen species.In this work,we report light-irradiation-modulated SMSI for enhanced formaldehyde(HCHO)oxidation.Specifically,the SMSI between Pt nanoparticles(NPs)and Bi_(2)MoO_(6)cre-ated surface-active oxygen at Pt-Bi_(2)MoO_(6)interfaces to activate HCHO to dioxymethylene(DOM).Notably,light irradiation boosted the SMSI and catalytic activity.Moreover,photogenerated holes in Bi_(2)MoO 6 im-proved HCHO adsorption and activation,while photogenerated electrons migrated from Bi_(2)MoO_(6)to Pt NPs to promote O_(2)adsorption and activation,accelerating the oxidation of DOM to CO_(2)and H_(2)O.The light-modulated SMSI and the synergy between photocatalysis and thermocatalysis lead to enhanced cat-alytic oxidation activity,providing a practical strategy for indoor volatile organic compound(VOC)de-composition under ambient conditions.

Formaldehyde oxidation on Pd/USY catalysts at room temperature: The effect of acid pretreatment on supports

The complete catalytic oxidation of formaldehyde (HCHO) to CO_(2)and H_(2)O at room temperature is a green route for indoor HCHO removal.Zeolite is an excellent carrier material for HCHO oxidation due to its large surface area,intricate pores and high adsorption capacity.However,the zeolite-supported noble metal catalysts have currently shown relatively low activity especially at room temperature.In this work,we present a facile acid treatment strategy for zeolite catalysts to improve the hydroxyl concentration and further enhance their catalytic activity for HCHO oxidation.Activity tests illustrated that HCHO could be completely oxidized to CO_(2)and H_(2)O at a nearly 100%conversion rate with a weight hourly space velocity (WHSV) of 150,000 mL/(g·hr) at 25℃,when the support of Pd/USY catalysts was pretreated by hydrochloric acid with a concentration of 0.20 mol/L.The characterization results revealed that the active hydroxyl groups originated from the dealumination in the acid treatment play a key role in the HCHO oxidation reaction.The deduced reaction mechanism suggests that bridging hydroxyl groups may oxidize HCHO to dioxymethylene(DOM) species and terminal hydroxyl groups are responsible for the transformation of DOM groups to formate (HCOO) species.

The effect of hydrogen reduction of α-MnO_(2) on formaldehyde oxidation: The roles of oxygen vacancies

A series of α-MnO_(2) catalysts with various Mn valence states were treated by hydrogen reduction for different periods of time. Their catalytic capacity for formaldehyde(HCHO) oxidation was evaluated. The results indicated that hydrogen reduction dramatically improves the catalytic performance of α-MnO_(2) in HCHO oxidation. The α-MnO_(2) sample reduced by hydrogen for 2 h possessed superior activity and could completely oxidize 150 ppm HCHO to CO_(2) and H_(2)O at 70℃. Multiple characterization results illustrated that hydrogen reduction contributed to the production of more oxygen vacancies. The oxygen vacancies on the catalyst surface enhanced the adsorption, activation and mobility of O_(2) molecules, and thereby enhanced HCHO catalytic oxidation. This study provides novel insight into the design of outstanding MnO_x catalysts for HCHO oxidation at low temperature.

Catalytic activities and mechanism of formaldehyde oxidation over gold supported on MnO2 microsphere catalysts at room temperature

MnO2 microspheres with various surface structures were prepared using the hydrothermal method, and Au/MnO2 catalysts were synthesized using the sol-gel method. We obtained three MnO2 microspheres and Au/MnO2 samples： coherent solid spheres covered with wire-like nanostructures, solid spheres with nanosheets, and hierarchical hollow microspheres with nanoplatelets and nanorods. We investigated the properties and catalytic activities of formaldehyde oxidation at room temperature. Crystalline structures of MnO2 are the main factor affecting the catalytic activities of these samples, and γ- MnO2 shows high catalytic performance. The excellent redox properties are responsible for the catalytic ability of γ-MnO2. The gold-supported interaction can change the redox properties of catalysts and accelerate surface oxygen species transition, which can account for the catalytic activity enhancement of Au/MnO2. We also studied intermediate species. The dioxymethylene （DOM） and formate species formed on the catalyst surface were considered intermediates, and were ultimately transformed into hydrocarbonate and carbonate and then decomposed into CO2. A proposed mechanism of formaldehyde oxidation over Au/MnO2 catalysts was also obtained.

Layered sphere-shaped TiO_2 capped with gold nanoparticles on structural defects and their catalysis of formaldehyde oxidation

We describe here a one-step method for the synthesis of Au/TiO2 nanosphere materials,which were formed by layered deposition of multiple anatase TiO2 nanosheets.The Au nanoparticles were stabilized by structural defects in each TiO2 nanosheet,including crystal steps and edges,thereby fixing the Au-TiO2 perimeter interface.Reactant transfer occurred along the gaps between these TiO2 nanosheet layers and in contact with catalytically active sites at the Au-TiO2 interface.The doped Au induced the formation of oxygen vacancies in the Au-TiO2 interface.Such vacancies are essential for generating active oxygen species（-＊O^-） on the TiO2 surface and Ti^3＋ ions in bulk TiO2.These ions can then form Ti^3＋-O^--Ti^4＋species,which are known to enhance the catalytic activity of formaldehyde（HCHO） oxidation.These studies on structural and oxygen vacancy defects in Au/TiO2 samples provide a theoretical foundation for the catalytic mechanism of HCHO oxidation on oxide-supported Au materials.

Preparation of birnessite-supported Pt nanoparticles and their application in catalytic oxidation of formaldehyde

Flaky and nanospherical birnessite and birnessite-supported Pt catalysts were successfully prepared and characterized by means of Xray diffraction （XRD）,transmission electron microscopy （TEM）,energy dispersive spectroscopy （EDS） and N2 adsorption-desorption.Effects of the birnessite morphology and Pt reduction method on the catalytic activity for the complete oxidation of formaldehyde （HCHO） were investigated.It was found that flaky birnessite exhibited higher catalytic activity than nanospherical birnessite.The promoting effect of Pt on the birnessite catalyst indicated that the reduction method of the Pt precursor greatly influenced the catalytic performance.Flaky birnessite-supported Pt nanoparticles reduced by KBH 4 showed the highest catalytic activity and could completely oxidize HCHO into CO2 and H2O at 50℃,whereas the sample reduced using H2-plasma showed lower activity for HCHO oxidation.The differences in catalytic activity of these materials were jointly attributed to the effects of pore structure,surface active sites exposed to HCHO and the dispersion of Pt nanoparticles.

Catalytic oxidation of formaldehyde over CeO2-Co3O4 catalysts

A series of CeO2-Co3O4 mixed oxide catalysts with different Co/（Co＋Ce） atomic ratios were synthesized by citric acid sol-gel method and used for catalytic oxidation of formaldehyde（HCHO）. Many techniques such as Brumauer-Emmett-Teller（BET）, X-ray diffraction（XRD）, scanning electron microscopy（FE-SEM）, temperature programmed reduction（H_2-TPR）, temperature-programmed desorption（O_2-TPD） and X-ray photoelectron spectroscopy（XPS） were used to characterize catalysts. The results of catalytic performance tests showed that the catalyst CeO_2-Co_3O_4 with Co/（Co＋Ce） ratio of 0.95 exhibited the best performance, and the temperature of complete oxidation of HCHO was 80 oC. The analytical results indicated that the addition of CeO_2 enhanced the specific surface area of Co_3O_4 and the fine dispersion of both of them. Moreover, the strong interaction between CeO_2 and Co_3O_4 resulted in the unique redox properties, which enhanced the available surface active oxygen and led to high valence state of cobalt oxide species. All those effects played crucial roles in the excellent performance of CeO_2-Co_3O_4 for the HCHO oxidation.