Study On The Preparation And Catalytic Performance Of Highly Efficiency Catalysts For The Oxidative Elimination Of Gaseous Pollutants

VOCs and CO are major pollutants in the air.They are not only harmful to human health,but also cause serious environment problems.Catalytic oxidation has been recognized as an effective way for VOCs and CO elimination due to its low energy consumption and without secondary pollution.Air as the oxygen resource and the products are CO₂ and H₂O.The highly efficient catalyst is the key factor in catalytic oxidation.Noble metal catalysts have shown high efficiency and good stability.However,the high cost limits their large-scale application.Non-noble metal catalysts are inexpensive,but the low efficiency unable to meet the large-scale demand in industry.In this paper,we prepared a series of low-price and high-efficiency catalysts.The prepared Pt-catalysts and manganese oxides all show excellent catalytic activity for toluene and CO oxidation.We explained the mechanism of molecular oxygen activation over the catalysts by investigating the internal relationship between the structure of catalysts and catalytic performance.The main contents are as follows:1.A highly efficient catalyst with low Pt content has been prepared by regulating the chemical state of Pt active sites and surface properties of supports.The optimized Pt/Al₂O₃ catalyst with Pt content as low as 0.1wt%can eliminate 1000 ppm toluene at180?with SV=24000 ml·g^-1·h^-1.The Pt/Al₂O₃ catalyst also exhibits excellent stability and moisture resistance,which means a great potential for application.The TOF value calculated based on the dispersion of Pt is 0.0685s^-1,representing a high utilization efficiency of Pt.A series of characterizations were employed to identify the key factors to influence the catalytic activity of Pt/Al₂O₃.And the role of Pt and Al₂O₃ in the activation of molecular oxygen and toluene are disclosed.DRIFT and EPR results indicate that Pt is the active center for oxygen activation.Metallic Pt particles can active molecular oxygen even at room temperature.Al₂O₃ offer the adsorption site for toluene and desorption site for CO₂.The weak and medium strength of acid-basic sites favorite the adsorption and desorption process during the reaction.Toluene oxidation over Pt/Al₂O₃ follows the modified L-H mechanism.The synergistic effect between metallic Pt particles and suitable Al₂O₃ support is the critical factor for the highly efficiency catalysts with low Pt content for toluene oxidation.2.Activation of O₂ is a critical step in heterogeneous catalytic oxidation,which directly influences the energy consumption of the whole reaction.Charge transfer from catalysts to O₂ molecules is an essential factor to control the energy barrier for O-O dissociation.Here,the concept of increased electron donors induced by nitrogen vacancy was adopted to propose an efficient strategy to develop highly active and stable catalysts for molecular O₂activation.Carbon nitride with nitrogen vacancies was developed as a promising support to construct a synergistic catalyst with Pt nanoparticles.Extensive characterizations combined with the first-principles calculations reveal that nitrogen vacancies with excess electrons could effectively stabilize metallic Pt nanoparticles by strong p-d coupling.The Pt atoms and the dangling carbon atoms surround the vacancy can synergistically donate electrons to the antibonding orbital of the adsorbed O₂.This synergistic catalyst shows great enhancement of catalytic oxidation performance and long-term stability.Particularly in emission control,the catalyst with 0.3wt%Pt could achieve the complete oxidation of toluene to CO₂ at 190?,which is about 30?lower than that of well-known Pt/Ce O₂.The activation energy was decreased to about 46 k J·mol^-1.Remarkably,the catalyst kept in air for 1 year still maintained the high activity and long-term operation stability?more than 200 h?like fresh ones.The introduction of electron-rich non-oxide substrate is an innovative strategy to develop active Pt-based oxidation catalysts,which could be conceivably extended to a variety of metal-based catalysts for catalytic oxidation.3.Non-noble metal catalysts have shown great potential in catalytic oxidation due to its low price and good performance.Among which,manganese oxides have been demonstrated to be one of the most promising catalysts for VOCs elimination.Despite of numerous works have been reported,the nature of high activity of manganese oxides,including the reaction mechanism remains to be intensive debate.Here,a series of Mn O_x/Al₂O₃ catalysts were prepared in oxide and reduce way,respectively.The oxidation states of manganese can be gradient controlled by regulating the loading amount of Mn.Systematic reaction results and characterizations demonstrated that a positive relationship exists between the catalytic activity and the average oxidation states?AOS?of Mn.The higher AOS of surface Mn atom,the better catalytic activity of CO and toluene oxidation.More than this,the bulk manganese oxide with different Mn valence also prove this conclusion.In the mix-valent manganese oxide,Mn atom with high AOS value contains more Mn⁴⁺species,more lattice oxygen species,and better low-temperature reducibility.The electron transfer between Mn⁴⁺/Mn³⁺or Mn⁴⁺/Mn²⁺weak the Mn-O bond,promotes the activation of surface lattice oxygen.Surface lattice oxygen act as the reactive oxygen species,the redox cycle of Mn species drives the exchange between surface lattice oxygen and molecular O₂.