本文選題：鉑-鐵 + 鉑-鈷��； 參考：《催化學(xué)報(bào)》2017年07期

【摘要】：負(fù)載型納米催化劑表面結(jié)構(gòu)與其催化性能之間關(guān)系的研究一直受到廣泛關(guān)注.由于其結(jié)構(gòu)復(fù)雜使得人們?cè)谘芯看呋瘎?gòu)效關(guān)系時(shí)遇到了很多困難.近年來(lái),大量研究發(fā)現(xiàn)反轉(zhuǎn)催化劑在眾多反應(yīng)中表現(xiàn)出優(yōu)越的催化性能.反轉(zhuǎn)催化劑是將過(guò)渡金屬氧化物負(fù)載于其它金屬表面.和傳統(tǒng)金屬/氧化物催化劑相比,反轉(zhuǎn)催化劑更能突出氧化物在催化反應(yīng)中的重要作用.眾多研究表明,在氧化物-金屬界面處存在特殊的作用,這種作用可以改變氧化物的電子特性和化學(xué)性質(zhì),進(jìn)而產(chǎn)生較高的催化性能.傅強(qiáng)等人創(chuàng)建了金屬氧化物負(fù)載于Pt表面的反轉(zhuǎn)催化體系,其表現(xiàn)出了高的低溫CO氧化反應(yīng)性能.在氧化物和Pt之間的界面限域效應(yīng)可以穩(wěn)定氧化物中配位不飽和的金屬陽(yáng)離子.這種配位不飽和的氧化物提供了活化O_2的活性位.目前,反轉(zhuǎn)催化劑的研究主要集中在單晶模型體系中,在負(fù)載型催化劑中的研究還較少.我們以炭黑(CB)為載體,將還原后的Pt-Fe和Pt-Co催化劑經(jīng)過(guò)酸洗制備了一種表面富Pt核為合金的結(jié)構(gòu).考察了酸洗后的Pt-Fe和Pt-Co催化劑經(jīng)過(guò)不同溫度氧化后的結(jié)構(gòu)變化,并討論了其結(jié)構(gòu)與CO完全氧化反應(yīng)(COOX)和CO選擇氧化反應(yīng)(CO-PROX)性能的關(guān)系.X射線粉末衍射(XRD),電感耦合等離子體發(fā)射光譜(ICP),透射電鏡(TEM)和X射線光電子能譜(XPS)表征結(jié)果表明,還原后的Pt基催化劑經(jīng)過(guò)酸洗可以選擇性去除納米粒子表面的3d過(guò)渡金屬,形成表面富Pt體相為合金的結(jié)構(gòu).將酸洗后的Pt-Fe和Pt-Co催化劑在不同溫度下空氣中氧化,發(fā)現(xiàn)近表層的Fe(Co)會(huì)擴(kuò)散到粒子表面上,形成過(guò)度氧化的Fe_2O_3(Co_3O_4)表面結(jié)構(gòu).氧化后的催化劑在COOX和CO-PROX反應(yīng)中表現(xiàn)出截然不同的催化性能.酸洗后的Pt-Fe(Pt-Co)催化劑經(jīng)過(guò)不同溫度氧化后在COOX反應(yīng)中活性都較差,室溫下的CO轉(zhuǎn)化率只有不到30%,CO完全轉(zhuǎn)化的溫度超過(guò)100 ℃,相當(dāng)于純Pt催化劑的活性.這說(shuō)明Pt表面過(guò)度氧化的Fe_2O_3(Co_3O_4)對(duì)CO氧化反應(yīng)的促進(jìn)作用不明顯.而氧化后的催化劑在CO-PROX反應(yīng)中表現(xiàn)出較高的活性,250 ℃(或350 ℃)氧化后的酸洗Pt-Fe催化劑室溫下的CO轉(zhuǎn)化率接近100%,250 ℃(或350 ℃)氧化后的酸洗Pt-Co催化劑室溫下的CO轉(zhuǎn)化率也達(dá)到了70%.結(jié)合表征和反應(yīng)結(jié)果,我們認(rèn)為氧化處理形成的表面過(guò)度氧化的金屬氧化物(Fe_2O_3,Co_3O_4)在COOX的催化性能較差.通入CO-PROX反應(yīng)氣后,氣氛中大量H_2的存在和Pt表面的氫溢流效應(yīng)可以使得表面Fe_2O_3,Co_3O_4在室溫下被還原成配位不飽和的FeO,CoO.這種配位不飽和的氧化物在表面Pt的限域作用和大量H_2氣氛下比較穩(wěn)定,并且具有較強(qiáng)的活化解離O_2的能力,進(jìn)而提高了CO-PROX反應(yīng)的活性.為了進(jìn)一步證實(shí)催化劑表面氧化物與其催化性能的關(guān)系,我們?cè)谑覝叵逻M(jìn)行了兩種反應(yīng)氣的循環(huán)實(shí)驗(yàn)測(cè)試.測(cè)試結(jié)果表明,對(duì)于氧化后的酸洗Pt-Fe催化劑,COOX反應(yīng)中的表面Fe_2O_3和CO-PROX反應(yīng)中的表面FeO可以通過(guò)變換反應(yīng)氣氛實(shí)現(xiàn)兩種氧化物的相互轉(zhuǎn)變,并表現(xiàn)出完全不同的催化性能.對(duì)于氧化后的酸洗Pt-Co催化劑,CO-PROX反應(yīng)中形成的CoO表面結(jié)構(gòu)在COOX反應(yīng)中也比較穩(wěn)定,在兩種反應(yīng)氣中表現(xiàn)出相似的催化性能.
[Abstract]:The study of the relationship between the surface structure and the catalytic performance of the supported nano catalyst has been widely concerned. Because of its complex structure, many difficulties have been encountered in the study of the structure effect relationship of the catalyst. In recent years, a large number of studies have found that the reverse catalyst has shown superior catalytic performance in many reactions. The transition metal oxide is loaded on the other metal surface. Compared with the traditional metal / oxide catalyst, the reverse catalyst can highlight the important role of the oxide in the catalytic reaction. Many studies have shown that there is a special role in the oxide metal interface, which can be used to change the electronic and chemical properties of the oxide. Fu Qiang et al. Created a reverse catalytic system with a metal oxide loaded on the Pt surface, showing a high low temperature CO oxidation reaction. The interface limit effect between oxide and Pt can stabilize the metal ionized metal ionon in the oxide, which is unsaturated. At present, the active sites of O_2 are activated. The research on the reverse catalyst is mainly concentrated in the single crystal model system, and the research on the supported catalyst is still less. We use carbon black (CB) as the carrier to prepare a Pt-Fe and Pt-Co catalyst after the reduction by acid washing. The Pt-Fe and Pt-Co catalysis after acid pickling are investigated. The structure changes after the oxidation of different temperatures, and the relationship between the structure and the properties of CO complete oxidation (COOX) and CO selective oxidation reaction (CO-PROX),.X ray powder diffraction (XRD), inductively coupled plasma emission spectroscopy (ICP), transmission electron microscopy (TEM) and X ray photoelectron spectroscopy (XPS) indicate that the Pt radical after reduction is shown. After pickling, the 3d transition metal on the surface of the nanoparticles can be selectively removed and the structure of the surface rich Pt phase is formed. The Pt-Fe and Pt-Co catalysts after acid washing are oxidized at different temperatures in the air. It is found that the near surface Fe (Co) will spread to the surface of the particles and form the surface structure of the over oxidation of Fe_2O_3 (Co_3O_4). After oxidation, the oxidation of Fe (Co_3O_4) is formed. The catalyst shows very different catalytic performance in the reaction of COOX and CO-PROX. After the acid washing, the Pt-Fe (Pt-Co) catalyst has poor activity in the COOX reaction after different temperatures, the CO conversion rate at room temperature is only less than 30%, the temperature of CO is more than 100 degrees C, and the activity of the pure Pt catalyst. This shows that the Pt surface is over. The oxidation of Fe_2O_3 (Co_3O_4) has no obvious promotion effect on CO oxidation, and the catalyst after oxidation shows high activity in CO-PROX reaction. The CO conversion rate of Pt-Fe catalyst after oxidation at 250 C (or 350 C) is close to 100% at room temperature and CO conversion rate at room temperature at 250 C (or 350 C) for acid washing Pt-Co catalyst at room temperature 70%. combined with characterization and reaction results, we believe that the catalytic performance of overoxidized metal oxides (Fe_2O_3, Co_3O_4) formed by the oxidation process is poor in COOX. After entering the CO-PROX reactant gas, the existence of a large number of H_2 in the atmosphere and the hydrogen overflow effect on the Pt surface can make the surface Fe_2O_3 and Co_3O_4 be reduced to match at room temperature. The unsaturated FeO, CoO., the ligand unsaturated oxides are stable in the confinement of the surface Pt and in a large number of H_2 atmospheres, and have strong ability to dissolve the O_2, and thus improve the activity of the CO-PROX reaction. In order to further confirm the relationship between the oxide of the catalyst surface and its catalytic performance, we conduct the reaction at room temperature. Two kinds of reactant gas cycle tests have been carried out. The results show that the surface FeO in the surface Fe_2O_3 and CO-PROX reaction in the COOX reaction can be converted to each other by changing the reaction atmosphere in the COOX reaction after the oxidation of the acid washing Pt-Fe catalyst, and shows a completely different catalytic performance. The surface structure of CoO formed by CO-PROX reaction is also stable in COOX reaction, showing similar catalytic performance in the two reaction gases.
【作者單位】： 安徽工業(yè)大學(xué)化學(xué)與化工學(xué)院;
【基金】：supported by the National Natural Science Foundation of China(21403004,21403003)~~
【分類號(hào)】：O643.36

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