【摘要】：負(fù)載型Pt基核殼催化劑在烷烴脫氫、CO氧化、氮氧化物還原等反應(yīng)中具有較好的催化性能,在催化領(lǐng)域得到了廣泛的應(yīng)用,負(fù)載型Pt基核殼催化劑的催化性能主要取決于金屬粒徑的大小以及載體的種類,Pt納米顆粒具有較高的表面能,高溫條件下容易發(fā)生團(tuán)聚現(xiàn)象,隨著Pt顆粒粒徑的增大催化劑的催化性能迅速降低。本論文從提高Pt納米催化劑的熱穩(wěn)定性出發(fā),利用Si02封裝金屬粒子的方法限制Pt粒子的團(tuán)聚,提高了催化劑的熱穩(wěn)定性,采用XRD、BET、TEM、SEM和TGA等方法對(duì)催化劑進(jìn)行表征,以對(duì)硝基苯酚的還原反應(yīng)為探針考察了Ptencap/mSiO2 (HSC550)、mSiO2/Pt/MOx/Fe和Fe@Pt/Ti(OH)4的催化性能,并取得了一些結(jié)論,具體內(nèi)容如下：1、通過NaBH4還原K2PtCl4制得Pt納米顆粒,負(fù)載于水熱法制得的碳球表面得到Pt/C,以CTAB為模板劑,TEOS為硅源在Pt/C表面封裝mSiO2層制得mSiO2/Pt/C,焙燒除去mSiO2/Pt/C中的碳球制備了HSC550中空催化劑。350℃焙燒后Pt/C表面的Pt顆粒己發(fā)生團(tuán)聚,mSiO2/Pt/C經(jīng)550℃焙燒后其中的Pt粒子并未發(fā)生明顯的團(tuán)聚現(xiàn)象,說明mSiO2對(duì)Pt粒子具有較好的保護(hù)作用,能有效提高催化劑的熱穩(wěn)定性。隨著焙燒溫度的升高,mSiO2/Pt/C中的碳球不斷除去,逐漸形成中空結(jié)構(gòu),HSC550催化對(duì)硝基苯酚還原反應(yīng)的催化活性最好,說明中空結(jié)構(gòu)可以提高HSC550的催化性能。HSC550重復(fù)使用5次之后催化對(duì)硝基苯酚還原反應(yīng)的催化活性并未明顯降低,該催化劑可以重復(fù)使用。2、分別以TBOT為前驅(qū)體制得納米TiO2、CeO2,負(fù)載于a-Fe2O3表面得到MOx/a-Fe2O3(M為Ti或Ce),將Pt納米顆粒負(fù)載于MOx/a-Fe2O3表面制得Pt/MOx/a-Fe2O3,在Pt/MOx/a-Fe2O3表面封裝mSiO2層制備了mSiO2/Pt/MOx/a-Fe2O3,對(duì)其進(jìn)行氫還原制得mSiO2/Pt/MOx/Fe核殼催化劑。在這個(gè)催化系統(tǒng)中,Pt顆粒被封裝在mSiO2層中,提高了mSiO2/Pt/MOx/Fe的熱穩(wěn)定性。500℃焙燒的mSi02/Pt/Ce02/Fe催化對(duì)硝基苯酚還原反應(yīng)的催化活性最好,隨著焙燒溫度升至700℃,mSiO2/Pt/CeO2/Fe中的納米Ce02和Pt顆粒部分發(fā)生團(tuán)聚,mSi02/Pt/Ce02/Fe催化對(duì)硝基苯酚還原反應(yīng)的催化活性明顯降低,說明mSi02/Pt/Ce02/Fe的抗焙燒性能較差。mSi02/Pt/Ti02/Fe經(jīng)700℃焙燒后催化活性并未明顯降低,說明mSiO2/Pt/TiO2/Fe具有較好的熱穩(wěn)定性。Ce02的功函數(shù)比TiO2低,電子富集區(qū)電子密度更大,500℃焙燒的mSiO2/Pt/CeO2/Fe催化活性最高。3、采用水熱法在α-Fe2O3表面包裹碳層得到α-Fe2O3@C,將Pt顆粒負(fù)載于α-Fe2O3@C表面得到α-Fe2O3@C/Pt,通過TBOT和TEOS的水解在a-Fe2O3@C/Pt表面先后包裹Ti02和mSiO2,制得α-Fe2O3@C/Pt/TiO2/mSiO2,焙燒除去碳層得到α-Fe2O3＠Pt/TiO2/mSiO2,利用強(qiáng)堿腐蝕a-Fe203@Pt/Ti02/mSi02中的Ti02得到a-Fe2O3@Pt/Ti(OH)4,對(duì)其進(jìn)行氫還原制得Fe@Pt/Ti(OH)4核殼催化劑。Fe核與Ti(OH)4納米棒之間出現(xiàn)空腔,Fe@Pt/Ti(OH)4中的Pt顆粒分布在Ti(OH)4納米棒之間,500℃焙燒后Pt顆粒不易團(tuán)聚,提高了Fe@Pt/Ti(OH)4的熱穩(wěn)定性。當(dāng)焙燒溫度達(dá)到700℃時(shí),Ti(OH)4納米棒分解為二氧化鈦得到Fe@Pt/TiO2,催化劑依然保持著核殼結(jié)構(gòu)。Fe@Pt/TiO2中的TiO2與Pt顆粒之間有較強(qiáng)的相互作用,其在對(duì)硝基苯酚的還原反應(yīng)中催化性能迅速提高,約為Fe@Pt/Ti(OH)4的1.5倍。
[Abstract]:The supported Pt-based core-shell catalyst has good catalytic performance in the reaction of alkane dehydrogenation, CO oxidation, nitrogen oxide reduction and the like, has been widely applied in the catalysis field, and the catalytic performance of the supported Pt-based core-shell catalyst mainly depends on the size of the metal particle size and the type of the carrier, The Pt nanoparticles have a high surface energy and can easily be agglomerated under high temperature conditions, and the catalytic performance of the catalyst is rapidly reduced with the increase of the particle size of the Pt particles. In order to improve the thermal stability of Pt nano-catalyst, the method of Si02 encapsulation of metal particles is used to limit the agglomeration of Pt particles, and the thermal stability of the catalyst is improved. The catalyst is characterized by XRD, BET, TEM, SEM and TGA. The catalytic properties of Ptencap/ mSiO2 (HSC550), mSiO2/ Pt/ MOx/ Fe and Fe@Pt/ Ti (OH)4 were investigated by the reduction reaction of p-nitrophenol, and some conclusions were obtained. And using CTAB as a template agent, TEOS is a silicon source to encapsulate the mSiO2 layer on the Pt/ C surface to obtain mSiO2/ Pt/ C, and the carbon spheres in the mSiO2/ Pt/ C are baked to remove the carbon spheres in the mSiO2/ Pt/ C to prepare the HSC550 hollow catalyst. It is shown that mSiO2 has a good protective effect on Pt particles, and can effectively improve the thermal stability of the catalyst. With the increase of the calcination temperature, the carbon spheres in mSiO2/ Pt/ C are continuously removed, the hollow structure is gradually formed, and the catalytic activity of the HSC550 for the reduction reaction of the nitrophenol is the best, and the catalytic performance of the HSC550 can be improved by using the hollow structure. the catalytic activity of the catalytic p-nitrophenol reduction reaction is not obviously reduced after 5 times of repeated use of the HSC550, and the catalyst can be used repeatedly;2, the nano TiO2 and the CeO2 are obtained by the TBOT as a precursor, and the MOx/ a-Fe2O3 (M is Ti or Ce) is obtained on the surface of the a-Fe2O3 respectively, The Pt/ MOx/ a-Fe2O3 is prepared by loading the Pt nano-particles on the surface of the MOx/ a-Fe2O3, and the mSiO2/ Pt/ MOx/ a-Fe2O3 is prepared on the surface of the Pt/ MOx/ a-Fe2O3, and the mSiO2/ Pt/ MOx/ a-Fe2O3 is prepared by hydrogen reduction to obtain the mSiO2/ Pt/ MOx/ Fe core-shell catalyst. In this catalytic system, Pt particles are encapsulated in the mSiO2 layer, and the thermal stability of mSiO2/ Pt/ MOx/ Fe is improved. The catalytic activity of mSi02/ Pt/ Ce02/ Fe on the reduction of nitrophenol was obviously reduced, and the anti-roasting property of mSi02/ Pt/ Ce02/ Fe was poor. The catalytic activity of mSi02/ Pt/ Ti02/ Fe was not significantly reduced after calcination at 700 鈩，

本文編號(hào)：2486343