Enhanced liquid phase catalytic hydrodechlorination of 2,4-dichlorophenol over mesoporous carbon supported Pd catalysts

Supported Pd catalysts on ordered mesoporous carbon (OMC) and activated carbon (AC) were prepared and their catalytic behavior for the liquid phase catalytic hydrodechlorination (HDC) of 2,4-dichlorophenol was investigated. In comparison with Pd/AC, Pd particles of Pd/OMC were effectively confined in the mesopores of OMC, resulting in high Pd dispersion and Pd²⁺ content. Accordingly, Pd/OMC exhibited higher catalytic activity than Pd/AC. Moreover, increasing catalyst reduction temperature lowered the catalytic activities and favored stepwise HDC of 2,4-dichlorophenol.     

载体预处理对Pd/C催化剂催化性能的影响

研究了活性炭硝酸表面改性对以其为载体制备的负载钯催化剂性能的影响。利用表面官能团滴定、N₂物理吸附和扫描电镜对催化剂进行表征，以邻硝基氯苯催化加氢制备2，2'-二氯氢化偶氮苯反应为模型反应对催化剂的性能进行评价。结果表明，经过不同浓度的HNO₃处理，活性炭孔结构性能变化不大，但是活性炭表面酸性含氧基团的浓度有了较大程度的增长，为Pd金属粒子的沉积提供了大量的吸附位，提高了Pd金属的分散度，从而制得高活性的Pd/C催化剂。通过30%HNO₃ 60 ℃水浴中回流4 h处理的活性炭可以达到最佳效果，所制得催化剂的活性是以未经硝酸处理过的活性炭载体制备的催化剂活性的2.3倍。     

载铁炭黑复合材料的制备与表征研究

采用浓硝酸对炭黑进行氧化,在炭黑表面引入含氧酸性基团后,利用酸性基团对铁离子的吸附性,通过离子交换和热解制备了一种铁/炭黑复合粒子。实验通过对炭黑表面酸性的滴定讨论了氧化时间及氧化温度对氧化程度的影响。EDS和TEM分析结果表明,铁/炭黑复合材料中无定形氧化铁在炭黑表面的含量可达40%,且分散均匀。     

活性炭表面改性对钌基氨合成催化剂的影响

研究了活性炭经HNO₃进行表面改性后对Ru/AC催化剂的影响。利用表面官能团滴定、N₂物理吸附和CO化学吸附方法对催化剂进行表征,并对催化剂进行氨合成活性评价。结果表明,活性炭经适量的HNO₃改性处理后,中孔有所增加,更主要的是增加了表面羧基,使活性炭的亲水性得到提高,从而提高了以水溶液浸渍法制备的Ru/AC催化剂的活性以及Ru的分散度;但过量HNO₃的改性处理会使活性炭表面不稳定基团增加,这些不稳定基团会降低Ru/AC催化剂的活性以及Ru的分散度。用5 mol·L^-1的HNO₃进行改性处理可以达到最优的效果。     

The catalytic hydrodechlorination of mono-, di- and trichlorobenzenes over supported nickel

The gas phase hydrodechlorination (HDC) of chlorobenzene (CB), chlorotoluene(s) (CT), 3-chlorophenol (3-CP), dichlorobenzene(s) (DCB) and trichlorobenzene(s) (TCB) over the temperature range 473 K≤T≤573 K has been studied using 1.5% and 6.1% (w/w) Ni/SiO₂ catalysts; the catalytic data have been obtained in the absence of any appreciable short-term deactivation. HDC of DCB and TCB generated the partially or the fully dechlorinated aromatic product + HCl and there was no significant cyclohexene or cyclohexane in the effluent stream. The conversion of mono-chloroarenes yielded the following reactivity sequence CB < 2-CT < 3-CT < 4-CT < 3-CP, i.e. the presence of an electron donating ring substituent enhances HDC and steric hindrance lowers reactivity. HDC kinetics have been adequately represented by a pseudo-first order approximation. Chlorine removal from DCB and TCB isomers proceeded through sequential and concerted routes, the relative importance of each dependent on the nature of the isomer and reaction conditions; apparent HDC activation energy increases in the order CB < DCB < TCB. The relationship between dechlorination selectivity and residence time/fractional conversion is addressed. The higher Ni loaded catalyst delivered consistently higher (specific) dechlorination rates and higher benzene yields from a polychlorinated feedstock. Catalytic HDC over Ni/SiO₂ is presented as a viable means of treating/detoxifying concentrated chlorinated gas streams and the best strategy for generating the parent benzene or a target partially dechlorinated product is discussed.     

Modification of Activated Carbon by the Basic Ionic Liquid [Bmim]OH: A Feasibility Study

The large amount of dye wastewater requires efficient techniques, e.g., adsorption by activated carbon (AC), for removal of dyes to decrease water pollution. AC was modified by the basic ionic liquid 1‐butyl‐3‐methylimidazolium hydroxide. The surface functional groups of AC changed evidently as detected by Fourier transform infrared spectroscopy and Boehm titration. To evaluate the influence of functional group change on adsorption performance, AC and modified activated carbon (MAC) were employed to remove methylene blue. The results indicated an increase of adsorbance with lapse of contact time. The adsorption capability of AC was distinctly higher than that of MAC. From kinetic studies it follows that the pseudo‐second‐order kinetic model can well describe the adsorption process.     

Effect of Carbon Deposits on Reactivity of Supported Pd Model Catalysts

Alumina-supported Pd model catalysts were prepared by Pd evaporation onto a thin alumina film grown on a NiAl(110) substrate. Adsorption and co-adsorption of ethene, CO and hydrogen on Pd/Al₂O₃/NiAl(110) covered by carbon species, formed by ethene dehydrogenation at 550 K, was studied by temperature programmed desorption (TPD). TPD results show that carbon deposits do not prevent adsorption but inhibit dehydrogenation of di- bonded ethene. Carbon species suppress CO adsorption in the highly coordinated sites and also suppress the formation of hydrogen ad-atoms on the surface. The ethene hydrogenation reaction performed by co-adsorption of hydrogen and ethene is inhibited by the presence of carbon deposits. The inhibition is independent of particle size studied (1-3 nm). The effects are rationalized in terms of a site-blocking behavior of carbon species occupying highly coordinated sites on the Pd surface.     

Oxidation of pinane over phthalocyanine complexes supported on activated carbon: Effect of the support surface treatment

The oxidation of cis-pinane with tert-butyl hydroperoxide, at room temperature and atmospheric pressure, was carried out in the presence of iron-phthalocyanines supported on activated carbons. The carbon supports were prepared from a NORIT activated carbon, which was modified by different chemical and thermal treatments (including oxidation in the gas and liquid phases). The carbon samples were characterized by nitrogen adsorption, mass titration and temperature programmed desorption (TPD). The TPD profiles were analysed by a simple deconvolution method, allowing for the determination of the amount of oxygen containing functional groups on the carbon surface. The main reaction product is 2-pinane hydroperoxide (77% selectivity at 91% conversion). Formation of 2-pinanol, pinocampheol and verbanol and the respective ketones was also observed. The influence of the surface chemistry of the carbon supports on catalytic activity and product selectivity is studied. The catalysts prepared from supports with very high or very low oxygen content exhibit low activity, whereas for supports with intermediate oxygen contents a good correlation between the amount of phenols and lactones and catalytic activity is obtained.     

Silver catalysts supported over activated carbons for the selective oxidation of CO in excess hydrogen: effects of different treatments on the supports

Commercial activated carbon (AC) was used as a support either in its original form or after various modifications, giving diverse textural and surface chemical characteristics. The changes of these properties were monitored by N₂ adsorption–desorption isotherms, temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Ag catalysts were prepared over the AC supports by a conventional wet impregnation method. The catalytic performances of supported Ag/AC catalysts in the selective oxidation of CO in excess H₂ were tested. The results indicate the textural and surface chemical characteristics are responsible for the different catalytic performances.     

钯(Ⅱ)-1,2-环己二胺配合物固载型催化剂的制备及催化合成碳酸二苯酯

采用椰壳活性炭为载体,通过质量分数20%HNO3氧化处理,在载体表面生成了0.383 mmol/g酚羟基,然后与N,N'-二[(三甲氧基硅)丙基]-1,2-环己二胺反应,引入了有机氮双齿配体,再与Pd(PhCN)2Cl2络合,ICP结果表明钯离子的固载量为0.79%。以FTIR、XPS及N2吸附-脱附等手段表征了催化剂制备过程中的各种中间体。在高压反应釜中以苯酚氧化羰基化法催化合成碳酸二苯酯(DPC),确定了最佳工艺条件为反应温度100℃、反应压力7.0 MPa、反应时间5 h及二氯甲烷为溶剂,并在最佳工艺条件下测得产物DPC收率为7.43%。该催化剂循环使用5次后DPC收率为6.75%。     

Characterization of the surface chemistry of carbon materials by potentiometric titrations and temperature-programmed desorption

Two methods currently used to characterize oxygen-containing functional groups on the surface of carbon materials are compared, namely potentiometric titration (PT) and temperature-programmed desorption (TPD). Two materials were used, activated carbon and multi-walled carbon nanotubes, which were subsequently modified by oxidative treatments in order to produce samples with different amounts of surface groups. The concentrations of carboxylic acid groups determined by both techniques are in good agreement, but the quantitative result obtained by TPD is closer to the analytical concentration of the species obtained by elemental analysis. Discrepancies between the quantitative results are more pronounced at higher pK_a values (weak acids), where the concentrations determined by PT are lower than those obtained by TPD. This directly reflects the effects of neglecting the electrostatic interaction parameter. The TPD method was particularly suited for the characterization of samples modified with ethylenediamine, which is anchored to specific oxygenated groups. PT results are useful to describe the material behaviour in aqueous solutions, where the activity of the surface groups depends not only on their concentrations, but also on their environment.     

Carbon activation with KOH as explored by temperature programmed techniques, and the effects of hydrogen

The effects of hydrogen produced upon KOH activation of an anthracite precursor were investigated by temperature programmed reaction (TPR) and post-carbonization temperature programmed desorption (TPD). TPR experiments performed with and without added hydrogen in the sweep gas for different KOH/anthracite ratios demonstrate that the greater this ratio, the greater the amount of hydrogen evolved during the activation process. It is also shown that hydrogen concentration during the activation process can significantly affect porosity development of the resultant activated carbon (AC). A series of post-activation TPD experiments was carried out for AC samples prepared under different conditions. The behavior of oxygen surface complexes in the TPD experiments also supports significant interaction between hydrogen and oxygen surface groups and/or inhibition of their formation. Post-activation gas evolution via thermal desorption is demonstrated to be an indicator of the hydrogen evolution during the activation process. These results explain earlier findings that porosity development correlates with hydrogen evolution, and is favored for high KOH/anthracite ratios, high sweep gas flow rates (up to a maximum value), and high activation temperatures. The effect of the “inert” sweep gas flow rate is attributed to the mass transfer rate of gas phase species, especially hydrogen and potassium vapor.     

氧化处理对碳纳米纤维及其负载钯催化剂性能的影响

采用混合的浓硝酸和浓硫酸处理石墨层排布为鱼骨类和平行类的碳纳米纤维,分别用X-射线衍射、电子显微镜和N2-物理吸附研究了氧化处理对碳纳米纤维石墨层结构和织构性质的影响;利用FT—IR、酸碱滴定和热重分析对碳纳米纤维表面引入的舍氧基团进行了研究。结果表明,经过氧化处理的碳纳米纤维仍然保持类石墨结构。但织构性质在激烈的氧化条件下发生显著的改变。氧化处理在碳纳米纤维表面引入了大量的羧基基团,并且随着氧化处理温度的升高表面引入的羧基基团密度增大。在相同的氧化条件下,鱼骨类碳纤维表面生成的羧基基团的量明显高于平行类碳纳米纤维。以氧气为氧化剂,在没有溶剂的情况下,碳纳米纤维负载的Pd催化剂在基甲醇氧化反应中具有很高的活性,并且碳纳米纤维表面的羧基基团对其负载的Pd催化剂活性有明显的促进作用。     

活性炭改性对用于甲酸分解的Pd/活性炭催化剂的影响

采用磁力搅拌法和水浴振荡法制备应用于甲酸分解的Pd/活性炭(AC)催化剂,研究了活性炭载体改性和制备方法对催化剂分解甲酸性能的影响。采用恒温水浴振荡装置,在80℃水浴中进行甲酸催化分解反应,以甲酸的催化分解率评价催化剂催化活性。结果表明,以经过不同的酸、碱、盐溶液改性后的活性炭为载体采用不同方法制备的Pd/AC催化剂对甲酸的催化分解效果不同,以Na2CO3改性的活性炭为载体采用磁力搅拌法制备的催化剂活性最好,甲酸水溶液的分解率达85%以上,含甲酸的工业废水的分解率达70%。     

Activated carbon as catalyst in wet oxidation of phenol: Effect of the oxidation reaction on the catalyst properties and stability

Catalytic wet oxidation (CWO) of phenol has been carried out in a continuous three-phase reactor by using a commercial activated carbon (AC) as catalyst, feeding oxygen as gas phase and an aqueous solution 1000 ppm in phenol to the reactor. A stable catalyst under operation conditions is one of the main difficulties to pass up in the catalytic wet oxidation process, so the stability of the activated carbon with the time on stream (TOS) was investigated. To do this the phenol conversion change was analyzed with TOS and results were contrasted to the change of the physicochemical properties of the AC with the TOS. Gas adsorption/desorption, TPD, XPS and SEM measurements were applied to the AC taken from the reactor after several TOS values. A significant reduction of the micro-pore volume and BET surface area of the catalyst was observed with TOS. However, as reaction proceeded the external surface area and the total amount of oxygen surface group increased. Moreover, regeneration of the initial catalyst properties was done by washing with water saturated in oxygen, at the reaction conditions or by heating in N₂ atmosphere at 450, 700 and 900 °C. The total micro-pore volume and internal surface area of the catalyst were not recovered by the regeneration process, probably due to blockage of the narrow micropores by pyrolytic carbon produced during the first step of the wet oxidation process.     

金属离子改性活性炭对二氯甲烷脱附活化能的影响

主要研究了金属离子改性活性炭对二氯甲烷脱附活化能的影响。通过浸渍法分别将6种不同金属离子负载在活性炭表面,采用ASAP 2010M测定该系列改性活性炭的孔径分布和比表面积,利用程序升温脱附技术测定了二氯甲烷在系列改性活性炭上的脱附活化能,应用软硬酸碱理论分析和讨论了活性炭表面负载不同金属离子对二氯甲烷脱附活化能的影响。结果表明,二氯甲烷在Al(Ⅲ)/SY-6AC、Li(Ⅰ)/SY-6AC、Mg(Ⅱ)/SY-6AC、Fe(Ⅲ)/SY-6AC和Ca(Ⅱ)/SY-6AC的脱附活化能高于其在原始活性炭上的脱附活化能,而它在 Ag(Ⅰ)/SY-6AC的脱附活化能低于在原始活性炭上的脱附活化能。根据软硬酸碱理论分类,二氯甲烷属硬碱,当活性炭表面分别负载了硬酸类金属离子Al³⁺、Li⁺、Mg²⁺、Fe³⁺和Ca²⁺,则增大了表面局部硬酸度,提高了对二氯甲烷的吸附能力; Ag⁺ 属软酸,当活性炭表面负载了Ag⁺,则降低了活性炭表面局部硬酸度,从而降低了对二氯甲烷的吸附能力。     

Adsorption removal of thiophene and dibenzothiophene from oils with activated carbon as adsorbent: effect of surface chemistry

Commercial coconut-based activated carbons (AC), before and after being treated using 65 wt% HNO₃ at different temperatures (termed as AC–Hs), were used as adsorbents to remove thiophene (T) or dibenzothiophene (DBT) from model oils. The fresh AC sample and all of the AC–Hs samples were characterized by Boehm titration, Fourier-transform infrared spectroscopy, and thermal analysis, which yield the information of the surface chemistry properties of the carbon materials. The results show that in comparison to the fresh AC sample, the quantity of oxygen-containing functional groups on the surface of AC–Hs samples increases as the pretreatment temperature of the fresh AC sample increases. The adsorption capabilities of the AC samples for removal of T and DBT from model oils were evaluated in a batch-type reactor. It has been found that the refractory DBT can be removed easily over the untreated commercial AC with the removal efficiency even being higher than that of T. In the case of acid modified AC–Hs samples, the efficiency for removal of T has been greatly improved, but this is not the case for the removal of DBT. The possible mechanism for adsorption removal of T and DBT over activated carbons is discussed in terms of the quantity of surface oxygen-containing functional groups of adsorbents and the chemical structure of sulfur compounds. The effect of olefin (1-octene) and aromatic hydrocarbons (benzene) in the model oils on the selective adsorption DBT over AC is also evaluated, revealing that in the case of DBT, the competitive adsorption is involved in the process, and the removal efficiency levels off at a level over 80%.     

微纳米多孔碳质材料的表面修饰及苯酚吸附性能

采用不同修饰工艺对微纳米多孔碳质材料进行处理,考察了修饰前后材料表面官能团的变化及其对苯酚吸附能力的影响,并结合Boehm滴定、Fourier变换红外光谱仪和X射线光电子能谱对材料表面官能团进行表征。结果表明：经高温（800℃）和尿素修饰后,材料的比表面积分别下降了41.9%和19.6%,苯酚吸附性能分别提升了21.2%和37%;经硝酸预改性的样品表面存在大量的羧基和酚羟基酸性基团,尿素改性时更利于吡啶和吡咯结构的生成。     

SO2 retention on CaO/activated carbon sorbents. Part II: Effect of the activated carbon support

The present paper analyses the role of the activated carbon (AC) properties on the SO₂ uptake capacity of CaO/AC sorbents prepared by AC impregnation or ionic exchange with calcium acetate water solutions. Gas adsorption and mercury porosimetry have been used for textural characterization of the AC and surface oxygen groups have been characterized by temperature programmed desorption (TPD). Thermogravimetry has been used for SO₂ retention tests and CO₂ chemisorption at 300 °C for CaO dispersion (d) determinations. The results show that the surface calcium on CaO/AC samples, determined as “Ca loading · CaO dispersion” (parameter Ca(%) · d), governs the SO₂ uptake. The surface oxygen content is the AC property that mainly controls both the calcium loading and surface calcium on CaO/AC samples, which could be explained by the fact that the surface oxygen lowers the hydrophobic character of the AC supports therefore favouring the interaction with the calcium acetate water solutions. The combination of high calcium loading and dispersion leads to SO₂ uptakes up to 123 mg SO₂/g. The textural properties of the supports have some influence in the calcium loading. However, the effect is masked by the blockage of AC porosity by the calcium loaded.