The Preparation And Performance Of Supported Noble Metal Composites For Catalytic Oxidation Of Formaldehyde At Room Temperature

Formaldehyde(HCHO)is one of the typical volatile organic compounds commonly detected in indoor environments,which poses a serious threat on human health.Therefore,it is of significance to remove HCHO from indoor environment to achieve a high indoor air quality.Room-temperature catalytic oxidation of HCHO has gained much attention due to the advantage that HCHO can be completely decomposed into carbon dioxide(CO2)and water without extra energy input,as well as the reusability of the catalysts.Currently,the supported noble metal catalysts are most used in the room-temperature oxidation of HCHO.It is generally considered that the catalytic activity of the catalyst is strongly influenced by the support.In order to achieve rational design and fabrication of high-performance catalyst for HCHO removal at room temperature,we prepared a series of supported noble metal catalysts for room-temperature removal of HCHO,and investigated the effects of the microstructure and surface hydroxyls on the performance of the catalysts.The main points are summarized as follows:(1)In this study,Pt supported on nanorod-shaped Co3O4(Pt/Co3O4)was prepared by calcination of microwave-assisted synthesized Co3O4 precursor followed by NaBH4-reduction of Pt precursor.The as-prepared Co3O4 exhibited a morphology of nanorods with lengths of 400–700 nm and diameters of approximately 40–50 nm,which were self-assembled by nanoparticles.The Pt/Co3O4 catalyst exhibited a superior catalytic performance for HCHO oxidation at room temperature compared to Pt supported on commercial Co3O4(Pt/Co3O4-c)and Pt supported on commercial Ti O2(Pt/Ti O2),which is mainly due to the high oxygen mobility resulting from its distinct nanorod morphology,strong metal-support interaction between Pt and Co3O4,and intrinsic redox nature of Co3O4 support.(2)A CeO2/Al OOH-supported Pt catalyst was prepared by combining the microemulsion-assisted synthesis of Al OOH and CeO2 hybrid with NaBH4-reduction of Pt precursor.The as-prepared catalyst obtained by depositing Pt nanoparticles on the CeO2/AlOOH(1:9 molar ratio)support(Pt/Al9Ce1)exhibited a remarkable catalytic activity and stability for oxidative removal of HCHO vapor at room temperature.The excellent performance of Pt/Al9Ce1 catalyst could be attributed to the abundance of surface hydroxyls,oxygen storage capacity in CeO2,high dispersion of Pt nanoparticles,and excellent adsorption performance of Al OOH.The mechanismof HCHO decomposition was investigated with respect to the behavior of adsorbed intermediates on the Pt/Al9Ce1 surface at room temperature using in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS).The results suggest that the main species formed on the surface during HCHO oxidation are the reaction intermediates,which could be directly oxidized to CO2 in the presence of O2.By taking advantage of high adsorption affinity of Al OOH nanoflakes toward HCHO,reducible ceria nanoparticles and excellent catalytic activity of Pt nanoparticles toward HCHO oxidation,it was possible to design a superior nanostructured catalyst for room temperature decomposition of HCHO.(3)Au nanoparticles(NPs)deposited on Al OOH support(Au/Al OOH)synthesized by microemulsion,microwave hydrothermal or hydrothermal method,was obtained via impregnation and NaBH4 reduction of Au precursor processes,and investigated to remove indoor HCHO pollutant at room temperature.It is found that Au supported on Al OOH prepared from microemulsion method(Au/Al OOH-m)exhibited the highest catalytic activity toward HCHO oxidation,followed by Au supported on Al OOH prepared from microwave hydrothermal method(Au/Al OOH-w),and Au supported on Al OOH prepared from hydrothermal method(Au/Al OOH-h)showed the lowest activity.Based on a variety of physical and chemical characterization results,the microstructure of Al OOH support,dispersion and size of Au NPs,surface hydroxyls,and interaction between Au and the support are important parameters for efficient removal of HCHO at room temperature.The superior catalytic performance of Au/Al OOH-m is attributed to its larger surface specific area,smaller size of Au NPs,higher amount of reactive surface hydroxyls,and better adsorption performance of the support.A catalytic mechanism involving the interaction between Au and Al OOH support,as well as the activation of O2 and surface hydroxyls,was proposed for HCHO complete oxidation over Au/AlOOH-m.(4)Hierarchical flower-like Pt/Ni Al-LDH catalysts with different [Ni2+]/[Al3+]molar ratios were synthesized with a hydrothermal method followed by NaBH4 reduction of Pt precursor at room temperature.The hierarchical flower-like Pt/Ni Al-LDHs were composed of interlaced nanoplates,and metallic Pt nanoparticles(NPs)approximately 3–4 nm in diameter were deposited on the surface of the Ni Al-LDHs with high dispersion.The as-prepared Pt/NiAl21 nanocomposite with a[Ni2+]/[Al3+] ratio of 2:1 was highly efficient in catalyzing the oxidation of HCHO into CO2 at room temperature.The high activity of the hierarchical Pt/NiAl21 nanocomposite was maintained after seven recycle tests,suggesting the high stability of the catalyst.Based on in situ diffuse DRIFTS studies,a reaction mechanism was put forward about HCHO decomposition at room temperature.(5)Fe2O3 nanoplate-graphene oxide(GO)supported Pt catalyst(Pt/GOFe)was synthesized by combining hydrothermal synthesis,impregnation and NaBH4 reduction processes,and investigated for removal of HCHO at room temperature.The presence of Pt nanoparticles and GO nanosheets in the as-prepared Pt/GOFe catalyst was confirmed by SEM,TEM,FTIR,Raman and XPS spectra.It was found that the addition of GO can alter the surface property of Fe2O3 nanoplate-supported Pt(Pt/Fe),and enhance its catalytic activity towards HCHO oxidation at room temperature.The superior catalytic performance of Pt/GOFe is attributed to the unique morphology of Fe2O3 nanoplates,abundance of oxygen functionalities and delocalized π bonds of GO,and plentiful surface oxygen species resulting from the interaction between Pt and GOFe.The in-situ DRIFTS revealed that surface oxygen species of Pt/GOFe could directly participate in the oxidation reaction of HCHO;the conversion of formate species into CO2 and H2O was the rate-determining step.The excellent catalytic performance and recyclability makes Pt/GOFe an efficient catalyst for HCHO oxidation at room temperature.