【摘要】：金屬Ru基催化劑在諸多催化反應(yīng)中獲得廣泛應(yīng)用,特別是在芳香族化合物的加氫反應(yīng)中顯示優(yōu)異的催化性能。近年來,研究者發(fā)現(xiàn)微觀限域結(jié)構(gòu)對金屬納米粒子與其周圍環(huán)境的相互作用方式及催化性能具有重要影響,由此指導(dǎo)人們設(shè)計出新型金屬納米及合金催化劑材料,充分發(fā)揮貴金屬的催化效能,滿足貴金屬催化劑高效利用的實際需求。本論文基于類水滑石(LDHs)主體層板的限域效應(yīng),采用尿素分解法首先制備了 RuMgAl-LDHs催化劑前體,然后通過氫氣氣氛下還原處理得到限域于LDHs層板中的金屬Ru納米粒子催化劑材料。進而,采用原位生長法在γ-Al203載體上合成出NiRuAl-LDHs前體,通過氫氣還原處理制備了負載型NiRu雙金屬合金催化劑材料。采用XRD、HRTEM、XPS及STEM-EDS等多種手段對限域結(jié)構(gòu)Ru納米粒子及NiRu合金的晶相組成、表面價態(tài)、形貌等進行表征和分析,進而推測了,探討了微量Ru的摻雜對金屬Ni的還原行為的影響。最后分別將Ru納米粒子催化劑及NiRu合金催化劑應(yīng)用于苯和裂解汽油模擬物的加氫反應(yīng)中,測試催化劑的活性、選擇性及穩(wěn)定性,并探討了催化劑結(jié)構(gòu)與反應(yīng)性能的構(gòu)效關(guān)系。主要的實驗內(nèi)容和結(jié)果如下:(1)采用尿素分解法制備了高結(jié)晶度的RuMgAl-LDHs催化劑前體,Ru離子均勻分布于水滑石層板中。然后,通過控制氫氣還原處理溫度制備了限域于LDHs層板中的金屬Ru納米粒子催化劑材料。采用HRTEM、STEM等表征研究表明,Ru納米粒子趨向于向LDHs邊緣區(qū)域聚集。此聚集趨勢在恒定pH法制備的小晶粒RuMgAl-LDHs前體中表現(xiàn)的更為明顯,由此制得選擇限域于LDHs邊棱部位的復(fù)合型納米金屬Ru/LDHs催化劑材料。將由不同還原溫度制備的Ru/LDHs樣品應(yīng)用于催化苯加氫生成環(huán)己烷反應(yīng)中,在90 ℃,5 MPa H2的反應(yīng)條件下,100℃還原樣品催化性能最佳。主要源于過低的還原溫度不能保證Ru粒子的邊緣遷移,而過高的還原溫度使得Ru顆粒在邊緣聚集長大,降低了金屬分散性。(2)以γ-Al2O3作為載體,采用原位生長法在其上合成了NiRuAl-LDHs前體,通過450 ℃下氫氣還原處理制備了負載型NiRu雙金屬合金催化劑材料。STEM-EDX、XPS、TPR等測試結(jié)果表明,NiRu雙金屬形成了合金結(jié)構(gòu),微量Ru的添加提高了 Ni2+的還原度,降低了 Ni粒子尺寸。將制備的不同Ru含量的負載型NiRu合金催化劑應(yīng)用于苯乙烯催化加氫反應(yīng)中。結(jié)果表明,微量Ru的摻雜明顯提高了 Ni催化劑的加氫反應(yīng)性能。推測Ru的添加提高了 Ni金屬分散性;同時,產(chǎn)生的溢流氫促使了催化性能的提高。
[Abstract]:Metal Ru catalysts have been widely used in many catalytic reactions, especially in hydrogenation of aromatic compounds. In recent years, researchers have found that the microstructure has an important influence on the interaction mode and catalytic performance between metal nanoparticles and their surrounding environment, thus guiding people to design new metal nanoparticles and alloy catalyst materials. Give full play to the catalytic efficiency of noble metals, meet the actual demand of high efficiency utilization of noble metal catalysts. In this paper, based on the limiting effect of hydrotalcite-like (LDHs) main plate, the precursor of RuMgAl-LDHs catalyst was prepared by urea decomposition method, and then the metal Ru nanoparticle catalyst material was prepared by reduction treatment in hydrogen atmosphere. Furthermore, the precursor of NiRuAl-LDHs was synthesized on 緯-Al203 carrier by in situ growth method, and the supported NiRu bimetallic catalyst material was prepared by hydrogen reduction. The crystal phase composition, surface valence state and morphology of limited structure Ru nanoparticles and NiRu alloys were characterized and analyzed by means of XRD,HRTEM,XPS and STEM-EDS, and the effect of trace Ru doping on the reduction behavior of Ni was discussed. Finally, Ru nanoparticles and NiRu alloy catalysts were applied to the hydrogenation of benzene and pyrolysis gasoline simulants, the activity, selectivity and stability of the catalysts were tested, and the structure-activity relationship between catalyst structure and reaction performance was discussed. The main experimental contents and results are as follows: (1) the precursor of RuMgAl-LDHs catalyst with high crystallinity was prepared by urea decomposition method. Ru ions were uniformly distributed in hydrotalcite laminates. Then, metal Ru nanoparticles were prepared by controlling the reduction temperature of hydrogen in LDHs laminates. HRTEM,STEM analysis showed that Ru nanoparticles tend to aggregate to the edge of LDHs. This aggregation trend is more obvious in the small grain RuMgAl-LDHs precursor prepared by the constant pH method. Therefore, the composite nanometallic Ru/LDHs catalyst material limited to the edge and edge of LDHs was prepared. The Ru/LDHs samples prepared at different reduction temperatures were used to catalyze the hydrogenation of benzene to cyclohexane. Under the reaction conditions of 90 鈩，

本文編號：2292999