负载型Pd-M催化剂在氯代苯酚加氢脱氯中的研究

发布时间：2019-01-21 07:16

【摘要】：随着化工业和农业的快速发展,水资源的污染问题正在日益严重,其中对水环境危害很大一类物质就是氯酚类有机化合物。它们能够直接或间接的危害人类的身体健康。目前催化还原法在脱除水中氯酚类有机物上具有经济、高效、能耗低、无污染等优点,是一项很值得研究探索的脱除水中氯酚类化合物的技术。本文采用分步浸渍法和共浸渍法法制备了多个系列Pd负载量为1%的Pd-In/γ-Al2O3,Pd-Cu/AC双金属催化剂及Pd-In-Cu/γ-Al2O3三金属催化剂,用于水中对氯苯酚加氢脱氯反应的研究。通过X射线衍射(XRD)、扫描电子显微镜-X射线色散能谱(SEM-EDS)、高分辨透射电子显微镜(HR-TEM)、X射线电子能谱(XPS)、程序升温还原(TPR)、H2脉冲化学吸附测定法等表征手段,对Pd、In、Cu金属颗粒的晶体结构、表面形貌、颗粒形状及粒径、分散度和表面积等进行了表征。反应在玻璃反应器中进行,加入对氯苯酚的水溶液和催化剂,通入H2进行反应,并用气相色谱对产物进行分析。考察了不同催化剂的制备方法,不同Pd-M摩尔比和不同催化剂载体对催化活性及选择性的影响。实验结果表明负载型铟钯双金属催化剂和铜钯双金属催化剂中的Pd、In和Pd、Cu金属粒子主要分布在载体表面。在Pd-In/γ-Al2O3催化剂中,Pd颗粒的粒径在2nm~5nm之间,随着铟钯摩尔比的升高,该系列催化剂的催化活性先增加后降低,主要因为向Pd单金属催化剂中添加适量的In助剂可以提高金属钯的分散度和表面积,其中先铟后钯制备的IP-2催化剂中Pd的分散度和表面积最大,能够达到41.6%和92.7m2g-1,而钯单金属催化剂中钯的分散度和表面积为23.7%和52.9m2g-1,但随着In含量的逐渐升高,催化剂中会生成铟钯合金,抑制了对氯苯酚的转化。在Pd-Cu/AC双金属催化剂中,Pd颗粒的粒径在1nm~6nm之间,随着铜钯摩尔比的升高,该系列催化剂的催化性能也是先增加后降低,主要原因是因为铜钯双金属催化剂中铜含量的变化,当铜含量低时,催化剂中的铜颗粒分散在钯颗粒之间,增大了其分散度和表面积,但随着铜含量的持续增加,在增大到一定值后铜颗粒开始覆盖在钯颗粒的表面上或与钯颗粒结合形成合金从而降低催化剂的活性。该系列催化剂中CP-2催化剂的分散度和表面积最大,分别为47.6%和106.2m2g-1,因此CP-2催化剂的活性也被证实是最好的,能够在30分钟内将对氯苯酚转化完全。与负载在氧化铝上的铜钯双金属催化剂相比,该系列催化剂的催化活性更高,主要是因为活性炭的表面积要明显高于氧化铝的表面积(活性炭表面积为704 m2 g-1,而氧化铝的表面积92.3m2 g-1),因此以活性炭为载体的催化剂比以氧化铝为载体的催化剂表现出了更高的分散度。又因为活性炭中没有金属的成分,因此当活性炭作为载体时,它与活性中心钯的相互作用比较弱,而相比之下氧化铝中的金属可能会与钯金属之间有较大的作用,因此以活性炭为载体的催化剂表现出了更高的催化活性。以活性炭负载的CP-2催化剂能在半小时内将对氯苯酚转化完全,而相同条件下,以氧化铝为载体的CP-1-2催化剂将对氯苯酚转化完全却需要一个小时。脱除水中对氯苯酚时,氧化铝做在载体的铟钯双金属催化剂中In/Pd摩尔比为0.1/1、先In后Pd浸渍法制备的IP-2催化剂脱除对氯苯酚的性能最优;活性炭做载体的Cu-Pd催化剂中,Cu/Pd摩尔比为0.3/1、先Cu后Pd浸渍法制备的CP-2催化剂脱除对氯苯酚的性能最佳。以上说明对氯苯酚的转化率主要与Pd的分散度和比表面有关,较高的Pd分散度可以提高催化剂的催化活性。负载型铜钯铟系列三金属催化剂对对氯苯酚的加氢脱氯反应的结果表明,三金属系列催化剂的催化活性比双金属催化剂的催化活性要低很多,混加型铟钯铜系列的三金属催化剂的催化性能要高于先铟后钯铜系列的三金属催化剂,而采用先铜后钯铟浸渍顺序制备的铜钯铟三金属催化剂在催化性能上则优于先铟后钯铜系列的三金属催化剂。
[Abstract]:With the rapid development of the chemical industry and the agriculture, the problem of water resource pollution is becoming more and more serious, in which the water environment is very harmful to a large class of substances, namely the chlorophenols organic compounds. They can directly or indirectly harm human health. The present catalytic reduction method has the advantages of economy, high efficiency, low energy consumption, no pollution and the like in the removal of chlorophenols in water, and is a technology which is well worth studying and exploring the removal of chlorophenol compounds in water. Pd-In/ Al-Al2O3, Pd-Cu/ AC bimetallic catalyst and Pd-In-Cu/ Al-Al2O3 three-metal catalyst with Pd loading of 1% and Pd-In-Cu/ Al-Al2O3 three-metal catalyst were prepared by step-by-step impregnation and co-impregnation. Pd and In are characterized by X-ray diffraction (XRD), scanning electron microscope-X-ray dispersion energy spectrum (SEM-EDS), high-resolution transmission electron microscope (HR-TEM), X-ray electron energy spectrum (XPS), program temperature-raising reduction (TPR), and H2 pulse chemical adsorption method. The crystal structure, surface morphology, particle shape and particle size, dispersity and surface area of Cu metal particles were characterized. The reaction was carried out in a glass reactor, an aqueous solution of p-chlorophenol and a catalyst were added, the reaction was carried out with H2, and the product was analyzed by gas chromatography. The preparation methods of different catalysts, the different Pd-M molar ratios and the effect of different catalyst carriers on the catalytic activity and selectivity were investigated. The results show that the Pd, In and Pd and Cu metal particles in the supported bimetallic catalyst and the copper-based bimetallic catalyst are mainly distributed on the surface of the carrier. In the Pd-In/ Al-Al2O3 catalyst, the particle size of the Pd particles is between 2nm and 5nm, and the catalytic activity of the series of catalysts is firstly increased with the increase of the molar ratio of the catalyst, mainly because the addition of an appropriate amount of In aid to the Pd single metal catalyst can improve the dispersity and the surface area of the metal catalyst, The dispersion and surface area of Pd in the IP-2 catalyst prepared by the preparation method are as high as 46.6% and 92.7m2g-1, while the dispersion and surface area of the catalyst in the monometallic catalyst are 23.7% and 529.9m2g-1, but with the increasing of In content, the conversion of p-chlorophenol is suppressed. in the Pd-Cu/ AC bimetallic catalyst, the particle size of the Pd particles is between 1nm and 6nm, and as the molar ratio of the copper is increased, the catalytic performance of the series of catalysts is also reduced, and the main reason is that the copper content in the copper-based bimetallic catalyst is changed, and when the copper content is low, the copper particles in the catalyst are dispersed between the nanoparticles, increasing its degree of dispersion and surface area, but as the copper content continues to increase, the copper particles begin to cover on the surface of the graphite particles or in combination with the graphite particles to form an alloy to reduce the activity of the catalyst as the copper content continues to increase. The dispersion and surface area of the CP-2 catalyst in the series of catalysts are respectively 47.6% and 106.2m2g-1, respectively, so the activity of the CP-2 catalyst is also proved to be the best, and the p-chlorophenol can be completely converted within 30 minutes. The catalytic activity of the series of catalysts is higher than that of the copper-based bimetallic catalyst supported on alumina, mainly because the surface area of the activated carbon is significantly higher than the surface area of the alumina (the surface area of the activated carbon is 704 m2 g-1, while the surface area of the alumina is 92.3m2 g-1), the catalyst with active carbon as the carrier shows a higher degree of dispersion than the catalyst supported by the alumina. because of the absence of a metal component in the activated carbon, when the activated carbon is used as the carrier, the interaction with the active center metal is relatively weak, and in contrast, the metal in the alumina may have a greater effect on the active carbon, Therefore, the catalyst with active carbon as the carrier shows higher catalytic activity. The CP-2 catalyst loaded with activated carbon can complete the conversion of the chlorophenol in half an hour, and under the same conditions, the CP-1-2 catalyst with the alumina as the carrier will need one hour for the conversion of the chlorophenol. in the removal of the p-chlorophenol in water, the molar ratio of the in/ Pd to the in/ Pd mole ratio of the alumina as the support is 0.1/ 1, the performance of the p-chlorophenol is optimized by the IP-2 catalyst prepared by the in-in Pd impregnation method, the Cu/ Pd molar ratio of the active carbon as a carrier is 0.3/ 1, The removal of p-chlorophenol with the CP-2 catalyst prepared by the pre-Cu-Pd impregnation method is the best. The above shows that the conversion of the chlorophenol is mainly related to the dispersion and specific surface of Pd, and the higher Pd dispersion can improve the catalytic activity of the catalyst. The results show that the catalytic activity of the three-metal-series catalyst is much lower than that of the bimetallic catalyst. The catalytic performance of the three-metal catalyst of the mixed-plus-iron-copper series is higher than the three-metal catalyst of the first copper-and-copper-copper series, and the copper-fired trimetal catalyst prepared by the impregnation sequence of the first copper and the second-metal catalyst is better than the three-metal catalyst of the first-step copper-fired copper-copper series.
【学位授予单位】：烟台大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O643.36

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