Low-temperature Catalytic Oxidation Of Formaldehyde And Carbon Monoxide Over Supported Pt Catalysts

Formaldehyde (HCHO) and carbon monoxide (CO) are regarded as the majorindoor pollutants, which are harmful to human health and air condition. Great effortshave been made to eliminate HCHO and CO in the indoor air in order to satisfy thestringent environmental regulations. Low-temperature catalytic oxidation is anattractive technique for removing these air pollutants. Especially,supported noblemetal catalysts are promising for their excellent catalytic oxidation properties atrelatively low reaction temperature. Currently, it is still a interesting subject todevelop highly efficient catalysts for low-temperature oxidation of HCHO and CO,and also more work is required for the purpose to clarify the nature of active centersof supported noble catalysts, and to underatand reaction mechanism.In this work, various supported Pt catalysts were prepared by adopting differentpreparation strategies (e.g., changing preparation methods, supports, and pretreatmentconditions). And their catalytic activities were investigated for the complete oxidationof HCHO and CO. A number of characterization means were carried out in order tobuild a clear relationship between the physicochemical properties of the catalysts andtheir catalytic oxidative performance. The main research contents and results are asfollows:1. Catalytic performance of HCHO oxidation over Pt/Fe₂O₃catalystsThe catalytic properties of iron oxide supported platinum catalysts (Pt/Fe₂O₃),prepared by a colloid deposition route, were investigated for the complete oxidation offormaldehyde. It is found that all the Pt/Fe₂O₃catalysts calcined at differenttemperatures (200-500℃) were active for the oxidation of formaldehyde. Amongthem, the catalysts calcined at lower temperatures (i.e.,200and300℃) exhibited relatively high catalytic activity and stability, which could completely oxidize HCHOeven at room temperature. Based on a variety of physical-chemical characterizationresults, it is proposed that the presence of suitable interaction between Pt particles andiron oxide supports, which is mainly in the form of Pt-O-Fe bonds, should play apositive role in determining the catalytic activity and stability of the supportedPt/Fe₂O₃catalysts.2. Catalytic performance of HCHO oxidation over Pt/SiO2-based catalystsA series of silica materials, including fumed SiO2, porous granular SiO2andmesoporous SBA-15, were adopted to prepare supported Pt catalysts by impregnationmethod. The catalytic properties of these silica supported Pt catalysts wereinvestigated for the complete oxidation of HCHO. Among them, fumed SiO2supported Pt catalyst (Pt/f-SiO2) shows very high catalytic activity, which couldcompletely oxidize HCHO even at ambient temperature. According to the results ofcatalyst characterization, it was proposed that the nature of silica supports could affectthe particle size and the chemical states of the platinum species and then furtherinfluence the redox property of Pt/SiO2-based catalysts. Compared with other silicasupported Pt catalysts, the Pt/f-SiO2catalyst possesses higher ratio of metallic Ptspecies, which might be a key factor in improving its capability to activate molecularoxygen, thus showing excellent catalytic activity in HCHO oxidation at lowtemperature.3. Research of nature active sites over Pt/Fe₂O₃catalysts in CO oxidationThe formation of Pt particles in small molecule organic media has been studied bytransmission electron microscopy and UV-visible spectrophotometry. Throughadjusting the synthesis conditions, Pt particles with various particle sizes could beeffectively prepared in the nanoscale. Based on the results of physicochemicalcharacterizations, the formation mechanism of the Pt particles has been proposed.A series of Pt/Fe₂O₃catalysts was prepared by a colloid deposition route, toinvestigate the structure of catalyst active sites and the mechanism of CO oxidation. A systematical study of supported Pt catalysts by means of transmission electronmicroscopy, X-ray photoelectron spectroscopy, temperature programmed reduction,time-resolved CO titration and in-situ DRIFT spectra is reported. The structure ofplatinum-support interface (i.e., Pt-O-Fe) was relatively easily formed over thePt/Fe₂O₃-b catalyst, which displayed high activity for CO oxidation at lowtemperature. Furthermore, the interaction (i.e., Pt-O-Fe) may also play a crucial rolein activating the oxygen species and weakening the intensity of CO-Pt bond at lowtemperature,showing excellent catalytic activity in CO oxidation at low temperature.