本文選題：一氧化碳氧化 + 金��； 參考：《催化學(xué)報(bào)》2016年11期

【摘要】：CO氧化可能是多相催化領(lǐng)域最常見(jiàn)的反應(yīng),它不僅能作為探針?lè)磻?yīng)研究催化劑結(jié)構(gòu)、反應(yīng)活性位等,而且在諸多實(shí)際過(guò)程如空氣凈化、汽車尾氣污染物控制、燃料電池所用氫源凈化等扮演重要角色.最早的CO氧化催化劑為霍加拉特劑,其組分主要為CuO與Mn O_2混合氧化物,然而在實(shí)際應(yīng)用過(guò)程中存在低溫活性低、吸濕易失活等缺點(diǎn).1987年,Haruta等發(fā)現(xiàn)濕化學(xué)法制備的氧化物負(fù)載Au催化劑表現(xiàn)出非常高的低溫CO氧化活性及耐水穩(wěn)定性,其Au粒子以納米尺度分散,進(jìn)而引發(fā)了催化研究領(lǐng)域的"淘金熱"及納米催化研究熱潮.而CO氧化通常作為考察Au催化劑結(jié)構(gòu)性質(zhì)的探針?lè)磻?yīng),也成為考核其它金屬催化劑是否具有高活性的判據(jù)之一.Pt族金屬上CO氧化反應(yīng)從Langmuir等研究開(kāi)始至今已有100多年,然而低溫下該金屬催化劑活性與Au催化劑相比要低一個(gè)數(shù)量級(jí).本質(zhì)原因?yàn)镻t族金屬上CO吸附較強(qiáng),O_2吸附與活化受到抑制,而該步驟被認(rèn)為是CO氧化的速控步,因而表現(xiàn)出較低的催化活性.通常Pt族金屬催化劑需要100 oC以上CO才能脫附,O_2進(jìn)而得以吸附.目前研究人員采取多種策略,其基本原則為削弱Pt族金屬上CO吸附強(qiáng)度或者提供其它活性位供O_2吸附與活化.本綜述將概括近十年來(lái)Pt族金屬催化劑CO氧化研究進(jìn)展,主要總結(jié)室溫甚至超低溫條件下的研究成果.高活性CO氧化催化劑主要是通過(guò)采用可還原氧化物為載體或助劑,或者改變催化劑表面性質(zhì)如使表面富OH基物種來(lái)形成.Au催化劑的研究發(fā)現(xiàn),改變金屬粒子尺寸極有可能獲得不同尋常的催化性能,而常規(guī)的Pt族金屬催化劑研究主要是在納米尺度.近期人們發(fā)現(xiàn)逐漸減小Pt族金屬粒子尺寸,從納米到亞納米甚至單原子時(shí),其電荷狀態(tài)逐漸呈正價(jià)形式,這有利于削弱其CO吸附強(qiáng)度.此外,可通過(guò)增強(qiáng)金屬載體間的相互作用,改變金屬載體接觸方式,如從核殼到交叉結(jié)聯(lián)結(jié)構(gòu),構(gòu)筑出更多的金屬載體界面,使得O_2更容易吸附與活化或穩(wěn)定更多的OH基物種進(jìn)而在此界面與吸附的CO反應(yīng).伴隨著表征技術(shù)的發(fā)展,CO氧化機(jī)理的認(rèn)識(shí)也更加深入,這給催化劑的設(shè)計(jì)帶來(lái)更多新的思路.(1)改變CO吸附活化位,將CO吸附活化位從金屬轉(zhuǎn)移到載體上,從而大大降低CO吸附強(qiáng)度,活化的CO物種在反應(yīng)過(guò)程中容易溢流到金屬載體界面處,這甚至有利于超低溫度下( 100℃左右)CO氧化.(2)改變O_2活化形式.O_2通常在Pt族金屬上容易以解離氧原子形式存在,通過(guò)改變載體、金屬載體界面性質(zhì)使得O_2以分子氧形式活化,如形成超氧或過(guò)氧物種,這有利于降低CO氧化的活化能壘,進(jìn)而提高其低溫甚至超低溫下CO氧化活性.今后,設(shè)計(jì)并合成出在超低溫度下能夠氧化CO的Pt族金屬催化劑將成為CO氧化催化劑研究的重要方向之一.
[Abstract]:Co oxidation is probably the most common reaction in the field of heterogeneous catalysis. It can not only be used as a probe to study catalyst structure and reactive sites, but also in many practical processes such as air purification and vehicle exhaust pollutant control. Hydrogen purification used in fuel cells plays an important role. The earliest catalyst for CO oxidation was Hogarat, the main component of which was CuO and MNO _ 2 mixed oxides. However, the low temperature activity was found in the practical application of CuO and MNO _ 2 mixed oxides. In 1987, Haruta et al found that the oxide supported au catalysts prepared by wet chemical method showed very high CO oxidation activity at low temperature and water resistance stability, and their au particles were dispersed in nanometer scale. This led to the gold rush and nano-catalysis research in the field of catalytic research. Co oxidation is usually used as a probe reaction to investigate the structure and properties of au catalysts. Co oxidation on Pt group metals has been studied for more than 100 years since Langmuir and so on. However, the activity of the metal catalyst at low temperature is one order of magnitude lower than that of au catalyst. The essential reason is that the adsorption and activation of CO on Pt group metals are inhibited, and this step is considered to be the rapid control step of CO oxidation, so it shows low catalytic activity. Usually Pt group metal catalysts require more than 100oC of CO to desorb O _ s _ 2 and then to be adsorbed. At present, researchers have adopted a variety of strategies, the basic principle of which is to reduce the adsorption strength of CO on Pt group metals or to provide other active sites for adsorption and activation of O _ (2). This review will summarize the progress in CO oxidation of Pt group metal catalysts in recent ten years, especially at room temperature and even at very low temperature. High activity CO oxidation catalyst is mainly found by using reductive oxide as carrier or auxiliary, or changing the surface properties of catalyst such as making the surface of the catalyst rich in OH group species to form .au catalyst. It is very possible to obtain unusual catalytic properties by changing the size of metal particles, while conventional Pt group metal catalysts are mainly studied at nanometer scale. Recently, it has been found that when the size of Pt group metal particles is gradually reduced, the charge state of Pt group metal particles is gradually in the form of positive valence from nanometer-sized to sub-nanoscale or even monoatomic, which is beneficial to weaken the adsorption intensity of CO. In addition, more metal carrier interfaces can be constructed by enhancing the interaction between metal carriers and changing the contact modes of metal carriers, such as from core-shell to cross-junction structures. It makes it easier for O _ s _ 2 to adsorb and activate or stabilize more OH group species and then react with adsorbed CO at this interface. With the development of characterization technology, the mechanism of CO oxidation is more deeply understood, which brings more new ideas to the design of catalyst. As a result, the adsorption intensity of CO is greatly reduced, and the activated CO species can easily overflow to the interface of the metal carrier during the reaction. This even helps to change the activation form of O _ (2) at ultra-low temperature (about 100 鈩，

本文編號(hào)：2021007