Investigation On Low Concentration Formaldehyde Catalytic Oxidation Removal

Formaldehyde?HCHO?is a typical indoor air pollutant and its removal is essential to protect public health and meet environmental regulations,indeed,long-term exposure to low concentrations of formaldehyde may lead to hazardous effects.Complete catalytic oxidation of formaldehyde has been proven to be an attractive technology attributed to high effectiveness in achieving total conversion of formaldehyde into harmless carbon dioxide and water without secondary pollution.A key requirement of this approach is the development of effective catalytic materials.Underlying the practical application for the elimination of low concentration formaldehyde,alkali metal-modified CoMn oxides were prepared for improving catalytic performance at low temperatures,additionally,Au-promoted AlOOH catalysts were synthesized for low-cost of noble metal in this work.The structure-activity relationship was in-depth discussion.Meanwhile,various characteristic techniques facilitated the elucidation of the reaction mechanisms.These results are expected to provide valuable guidance for the rational design of low-cost and stable catalysts with highly efficiency for HCHO elimination.The findings were summarized as follows:To promote the catalytic activity of formaldehyde at low temperatures for non-noble metal oxide catalysts,alkali-modified CoMn catalyst system was constructed in this work.Na and K-doped CoMn oxides greatly enhanced the low temperature activities,nearly 100%HCHO conversion was obtained at 60 ^oC?WHSV=60000 ml/g/h?over K-doped CoMn oxide,and 23%of HCHO was oxidized to CO₂ at RT,representing one of the best results for HCHO oxidation among non-noble catalysts.XPS and H₂-TPR evidenced an increase in surface adsorbed oxygen species upon doping K into CoMn oxides,the amount of which has a linear relationship with the HCHO oxidation rate at low temperatures.This gives clear evidence that surface active oxygen species contrust the reaction site of HCHO oxidation.What is more,surface hydroxyl species were formed from the dissociation of H₂O with the promoting effect of K as proved by in situ DRIFTS,thereby creating a new reaction pathway.Notably,the surface hydroxyl species was found to facilitate the simultaneous generation of hydrocarbonate intermediates as well as the consumption of such intermediates,therefore enhancing the activities of CoMnK.Indeed,the presence of water mainly promoted the reaction pathway of formaldehyde oxidation at low temperatures on CoMnK catalyst and decreased the activation energy of formaldehyde oxidation reaction.To overcome the obstacle of high-cost of noble metals,the Al₂O₃ supports in some specific morphologies and AlOOH support are expected to promote the performance of the Au-promoted catalysts for the elimination of formaldehyde at RT.The Au/AlOOH possessing abundant surface hydroxyl groups was synthesized by urea homogeneous deposition precipitation method.The results suggested that 0.5 wt%Au-promoted AlOOH exhibit almost86%HCHO conversion at RT?WHSV=75,000 ml/g/h,RH=50%?.FT-IR measurements evidenced an increase of hydroxyl amount of AlOOH compared with Al₂O₃.The result also help defined the two types of hydroxyl groups entity in AlOOH in both free and associated states.The hydroxyl groups in associated state were pivotal to the stabilization of nano gold.Therefore the synergetic effect between the metal and support promoted the highly dispersion of Au,thereby enhancing the activity of 0.5 wt%Au/AlOOH at RT.