One-step Synthesis Of Noble Metal Doped MCM-41 Mesoporous Silica Materials And Their Performances Of Toluene Catalytic Oxidation

Volatile Organic Compounds (VOCs), mainly produced from vehicle exhausts, industrial processes and landfill disposal, are one kind of main air pollutants. VOCs produced by industrial production in China were characterized as low concerntration and large flow rate. In view of this, the catalytic oxidation treatment technology for VOCs emissons control attracted many attentions due to its high efficiency, low energy consumption and less secondary pollution. The key point of catalytic oxidation technology was the development of high-performance catalysts. Noble metal based catalysts exhibited high catalytic activity in VOCs catalytic oxidation in comparison with transition metal oxides. However, agglomeration of noble metal particles limits its application in practical application. MCM-41 silica mesoporoous materials were supposed to be a promising support in catalytic application due to its huge specific surface area, large pore volume and well stablity. In this paper, a series of Pt-Pd and Pt-Zr modified mesoporous MCM-41 samples catalysts have been prepared via one-step synthesis method for VOCs total oxidation in order to improve the dispersion of doped noble metals. The main content of this work focus on the evaluation of the catalytic activities (toluene was selected as the probe molecule) for different samples and the relationship between physicochemical properties of the samples and the activities.Firstly, we have prepared a series of bimetallic Pt-Pd/MCM-41 catalysts by one-step synthesis method. The obtained catalysts were referred to Pt x wt%-Pd y wt%/MCM-41 (x+y=0.3). The acitivity tests showed that as-synthesized bimetallic Pt-Pd/MCM-41 samples were of a higher catalytic efficiency comparing to monometallic Pt or Pd/MCM-41 catalyst towards toluene catalytic oxidaton. Further characterization studies indicated that there existed a strong synergistic effect of the two noble metals during the one-step synthesis process for bimetallic samples. TEM restults illustrated that Pt0.2wt%-Pd0.1wt%/MCM-41 sample showed a better distribution of noble metals with smaller particle size comparing to monometallic samples, hence increasing the active surface area. XPS study indicated that the addition of Pd species leading to the rising of surface Pt(0) content. The above-mentioned two aspects would enhance the oxygen carrying capacity and reducibility of Pt-Pd/MCM-41 bimetallic catalysts, thereby resulting in the improvement of catalytic activity. In addition, Pt-Pd/MCM-41 catalysts also exhabited a very good stability performance.After that, a series of Pt0.3wt%-Zr x wt%/MCM-41(x=1,3,5) were also prepared by the same method. The catalytic activityies of these samples were found increased at an elevated Zr content and Pt0.3wt%-Zr5wt%/MCM-41 exhibited the best catalytic activity among these samples. The characterization results showed that the acidity of the Pt-Zr/MCM-41 catalysts espeially the Lewis acidity was grealty strengthened with Zr incorporation, which would be beneficial to the adsorption of toluene during the catalytic reaction, which was considered as the main cause of its enhanced catatatic activity. In addition, the incorporation of Zr can somewhat facilitate the dispersion of Pt, which can affect the catalyst reducibility, oxygen carrying capacity. This is also one of the reasons of the improvement of catalytic activity for toluene oxidation.