Hydrodenitrification with PdCu Catalysts: Catalyst Optimization by Experimental and Quantum Chemical Approaches

A continuous process for nitrate and nitrite abatement from drinking water by catalytic hydrogenation has been developed in our lab. We describe the experimental process development procedure, and support it with semiempirical quantum chemical methods. Comparisons of activated carbon (ACC) and silica glass fiber (GFC) cloths as supports for mono- and bimetallic Pd-Cu catalysts show the former to be 45-fold and 15-fold more active for nitrite and nitrate hydrogenation, respectively, than the latter. Catalysts prepared by selective deposition of Cu on Pd/ACC led to better activity for nitrate hydrogenation than catalysts prepared by co-impregnation or ion exchange methods. The optimal Cu:Pd atomic ratio was found to be 1:2. The computational results show the following: (i) The dispersion of Pd catalysts supported on ACC is much higher than that on GFC due to the larger surface area and higher density of adsorption sites, and that accounts for the higher activity of PdCu/ACC; (ii) Nanosized Pd particles supported on ACC have a semispherical shape and possess preferentially close-packed triangular surfaces, while Pd/GFC particles are extended in the direction parallel to the support surface and show both fcc (100) and (111) planes; (iii) The interaction of Cu atoms with both supports is stronger than that of Pd; adsorbed Cu atoms show a greater ability to form monometallic than bimetallic bonds and that should result in poor mixing of the metal upon co-impregnation, as was observed experimentally; (iv) Cu atoms in bimetallic PdCu particles admit a significant positive charge; the experimentally measured solubility of metal atoms correlates with their calculated charges. The best catalyst (2 wt%Pd-0.6 wt%Cu/ACC) was employed in a novel continuous flow reactor for nitrate hydrogenation in distilled and tap water. The advantages of the reactor investigated over a conventional packed bed reactor are discussed, suggesting a potential for further process intensification.     

Thermal behavior of the phenol-Pd-ACC system

Thermal behavior, morphology features and phenol adsorption as well as Pd catalytic properties in activated carbon cloth (ACC)-Pd-Phenol system and its subsystems were investigated under oxidizing and inert atmospheres. Pd/ACC systems were classified in two types: systems with low Pd loadings (Pd <1.3% wt.) were found to be more active than systems with high Pd loading. Thermal behavior of the systems was described using characteristic temperatures marking the initiation of phenol oxidation (T_p), ACC surface oxidation (T_c) and the carbon gasification (T_g). Analysis of the DTA/TGA profiles was interpreted in terms of desorption, carbonization, oxidative coupling reactions and complete combustion. Data on thermal behavior of systems in argon and air demonstrated a significant catalytic activity of impregnated Pd towards oxidation of ACC surface and its skeleton, and the processes of the phenol/ACC carbonization and oxidation. The results obtained are the basis for development of thermal and catalytic regeneration processes for ACC adsorbent.     

Adsorption of Phenol and 2,4‐Dinitrophenol on Activated Carbon Cloth: The Influence of Sorbent Surface Acidity and pH

Abstract

In this work the effect of the activated carbon cloth surface acidity and pH of the solution on phenols adsorption has been studied. Two phenols, widely different in the terms of their pKa values (phenol and 2,4‐dinitrophenol), have been chosen as the model compounds. It has been shown that phenol adsorption was favored by low pH values of solution and high point of zero charge values of activated carbon cloths. The adsorption of 2,4‐dinitrophenol was promoted at very low pH values of solution and it was less influenced by activated carbon cloth surface acidity.     

Activated Carbon Fiber Cloth/Biomimetic Apatite: A Dual Drug Delivery System

A biomaterial that is both bioactive and capable of controlled drug release is highly attractive for bone regeneration. In previous works, we demonstrated the possibility of combining activated carbon fiber cloth (ACC) and biomimetic apatite (such as calcium-deficient hydroxyapatite (CDA)) to develop an efficient material for bone regeneration. The aim to use the adsorption properties of an activated carbon/biomimetic apatite composite to synthetize a biomaterial to be used as a controlled drug release system after implantation. The adsorption and desorption of tetracycline and aspirin were first investigated in the ACC and CDA components and then on ACC/CDA composite. The results showed that drug adsorption and release are dependent on the adsorbent material and the drug polarity/hydrophilicity, leading to two distinct modes of drug adsorption and release. Consequently, a double adsorption approach was successfully performed, leading to a multifunctional and innovative ACC-aspirin/CDA-tetracycline implantable biomaterial. In a second step, in vitro tests emphasized a better affinity of the drug (tetracycline or aspirin)-loaded ACC/CDA materials towards human primary osteoblast viability and proliferation. Then, in vivo experiments on a large cortical bone defect in rats was carried out to test biocompatibility and bone regeneration ability. Data clearly highlighted a significant acceleration of bone reconstruction in the presence of the ACC/CDA patch. The ability of the aspirin-loaded ACC/CDA material to release the drug in situ for improving bone healing was also underlined, as a proof of concept. This work highlights the possibility of bone patches with controlled (multi)drug release features being used for bone tissue repair.     

Low-temperature methanol synthesis from carbon dioxide and hydrogen via formic ester

A new route of methanol synthesis, at 443 K and under pressurized conditions, from carbon dioxide and hydrogen through formic ester was investigated, by using Cu-based catalysts. This one-pot reaction consisted of three steps:

1. formic acid synthesis from CO₂ and H₂,

2. esterification of formic acid by ethanol to ethyl formate, and

3. hydrogenolysis of ethyl formate to methanol and ethanol.

活性炭纤维布吸附与电热脱附挥发性有机化合物研究进展(英文)

A general research program,focusing on activated carbon fiber cloths(ACFC) and felt for environmental protection was performed.The objectives were multiple:(i) a better understanding of the adsorption mechanisms of these kinds of materials;(ii) the specification and optimization of new processes using these adsorbents;(iii) the modeling of the adsorption of organic pollutants using both the usual and original approaches;(iv) applications of ACFC in industrial processes.The general question was:how can activated carbon fiber cloths and felts be used in air treatment processes for the protection of environment.In order to provide an answer,different approaches were adopted.The materials(ACFC) were characterized in terms of macro structure and internal porosity.Specific studies were performed to get the air flow pattern through the fabrics.Head loss data were generated and modeled as a function of air velocity.The performances of ACF to remove volatile organic compounds(VOCs) were approached with the adsorption isotherms and breakthrough curves in various operating conditions.Regeneration by Joule effect shows a homogenous heating of adsorber modules with rolled or pleated layers.Examples of industrial developments were presented showing an interesting technology for the removal of VOCs,such as dichloromethane,benzene,isopropyl alcohol and toluene,alone or in a complex mixture.     

Cloth catalysts for water denitrification: II. Removal of nitrates using Pd–Cu supported on glass fibers

The use of glass fibers in the form of woven cloth (GFC), as a new type of catalytic support, was studied for the reduction of aqueous nitrate solutions using a Pd/Cu–GFC catalyst. The activity (per gram Pd) and selectivity to nitrogen were found to be comparable with those found for Pd–Cu catalysts supported on the other carriers. The maximal initial removal activity was found for a catalyst with a Pd/(Pd+Cu) ratio of 0.81. The corresponding activity was 0.7 mmol min⁻¹ (g_Pd)⁻¹, and the selectivity was 97 mol% at 25°C and pH 6.5 for initial nitrate concentration of 100 mg l⁻¹. The selectivity to nitrogen declined at high conversions of nitrate and high pH.     

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.     

Structured but not over-structured: Woven active carbon fibre matt catalyst

Catalytic hydrogenation of citral was studied on a Pt on active carbon cloth (ACC) catalyst, with a Pd in ionic liquid on ACC and a commercial Pt on active carbon powder catalysts. The metal was supported on active carbon either by direct impregnation or utilizing the ionic liquid as the intermediate phase on the carbon. The influence on selectivity and activity, of the most important variables, such as temperature and pressure, was investigated in a batch reactor. Four consecutive experiments were carried out with each catalyst. The aim with the reuse of catalysts in the batch reactor was to elucidate eventual catalyst deactivation. The decrease in activity was very notable in the case of traditional impregnated catalysts, whereas the novel SSIL-TM (structured supported ionic liquid-transition metal) or Pd in ionic liquid on active carbon essentially maintained its activity in four consecutive batches. The catalysts were characterized with scanning electron microscopy, N₂ physisorption, and inductively coupled plasma analysis combined with mass spectroscopy. With the Pt on active carbon fibre catalyst, 80–100% selectivity of carbonyl group hydrogenation was achieved at 15% conversion, whereas the Pd in ionic liquid on ACC catalyst displayed an impressive metal efficiency (citral-to-Pd ratio of 156, mol:mol), selectivity (45%) and activity (92% conversion at 140 min) as well as tolerance towards catalyst deactivation. Supported ionic liquids provide a new reaction environment for catalytic transformations.     

Adsorption and electrothermal desorption of organic vapors using activated carbon adsorbents with novel morphologies

Novel morphologies of activated carbons such as monolith, beads and fiber cloth can effectively capture organic vapors from industrial sources. These adsorbent materials are also unique because they can undergo direct electrothermal regeneration to recover the adsorbed organic vapors for potential re-use. This investigation compares and contrasts the properties of these adsorbents when using electrothermal-swing adsorption. The adsorption systems consisted of an organic vapor generation system, an electrothermal-swing adsorption vessel, a gas detection unit, and a data acquisition and control system. The activated carbon monolith (ACM) had the lowest pressure drop, highest permeability, highest electrical resistivity and lowest cost as compared to the activated carbon beads (ACB) and the activated carbon fiber cloth (ACFC). ACB had the largest throughput ratio and lowest length of unused bed as compared to the other adsorbents. However, ACFC had the largest adsorption capacity for toluene when compared to ACM and ACB. ACFC was also faster to regenerate and had a larger concentration factor than ACM and ACB. These results describe relevant physical, electrical, adsorption and cost properties for specific morphologies of the adsorbents to more effectively capture and recover organic vapors from gas streams.     

An assessment of activated carbon cloth microporosity change due to chemical activation

Controlled modification of micropore volumes of samples from the FM1-series of activated carbon cloth can be achieved via selective oxidation: strong caustic treatment leads to an increase in volume, while peroxydisulfate treatment leads to a decrease in volume. Pore volume increases are determined to be due to inorganic content leaching, determined via XPS analyses, developing small primary micropores for the least activated carbon cloth (FM1/250) and a widening of the pore width for the most activated carbon cloth (FM1/700). All cloths exhibited Type I nitrogen adsorption isotherms both prior to and post oxidative treatment.     

竹炭和各种炭布的制备工艺及其应用

采用特殊烧制工艺制得的优质竹炭，比表面积高达700m^2／g。将竹炭制成0．5～100微米的超细微粉，与多种高分子材料结合，可制成许多种高分子复合材料——各种具有不同性能、不同用途和不同类型的炭布，这些炭布具有极好的催化活化、吸附分解、吸湿干燥和除臭抗菌等性能。利用这些炭布，已成功地开发了一系列功能产品。     

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。     

单股流布水改性碳钢表面的润湿特性

湿式静电除尘技术收尘极表面的易腐蚀和水膜均布问题是影响该技术连续可靠运行的重要因素。针对这两个问题,对碳素钢冷轧成型板进行了抗腐蚀保护层和在保护层基础上黏附不同附加亲水层的改性。使用称重法和平面成像法进行了单股流布水不同Reynolds数下不同改性表面持液量、表面流量、成膜率、水膜平均厚度等润湿特性的研究。结果表明:抗腐蚀保护层降低基材的润湿特性,附加亲水层中台丽碳纤维布的持液量较基材碳钢表面增加1.0～2.2倍,细沙粒成膜率比基材碳钢增加50%～60%,水膜厚度均在0.3～0.7 mm之间(最大达1.4 mm);玻璃纤维布黏附在环氧树脂表面的疏松程度直接影响表面的润湿特性,涂刷第3层环氧树脂后自然晾晒12 h,120℃加热1 h后敷设玻纤布,自然冷却至固化得到的表面润湿特性最佳,其持液量可达0.014～0.021 g·cm^-2,临界饱和时间 < 3 min,实现完全润湿,成膜率较基材增加34～40倍;改性材料表面布水参数:喷水孔间距≥10 cm、Reynolds数超过2000,此时表面液膜为波动层流,可获得理想冲刷效果。     

Surface chemistry of a viscose-based activated carbon cloth modified by treatment with ammonia and steam

The influence of ammonia treatment at 800 °C on the catalytic activity of a viscose-based activated carbon cloth (ACC) was evaluated for the oxidative retention of H₂S or SO₂ at room temperature. Change in the surface chemistry was observed by X-ray spectroscopy of nitrogen (N1s) and by temperature programmed desorption (TPD). Dynamic adsorption of H₂S or SO₂ in moist air onto a packed bed of activated carbon cloth was monitored by measurement of the breakthrough curves at room temperature. ACC modified by ammonia showed noteworthy enhanced SO₂ and H₂S loading relative to the untreated ACC. Improved SO₂ retention rate could be replicated several times after regeneration by washing at room temperature, in contrast to the case with H₂S. The likely reasons for the behavior of H₂S and SO₂ on the ammonia-treated ACC are discussed with reference to the recent literature.     

Removal of thiophenic compounds from liquid fuel by different modified activated carbon cloths

The adsorption behavior of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) from n-heptane was investigated onto activated carbon cloth (ACC) and its modified forms at 30 °C in batch condition. ACC was modified by HNO₃, (NH₄)₂S₂O₈, H₂SO₄, HCl and NaOH at ambient temperature. The adsorbents were characterized using nitrogen adsorption/desorption. It was found that the adsorbents are mainly microporous but differ in their surface chemistry, which is related to the effect of oxidizing agent. The adsorption process was studied from both equilibrium and kinetics point of view. The equilibrium experimental data were fitted to the Langmuir, Freundlich and Langmuir-Freundlich by non-linear method. Among the tested adsorbents, the modified ACC with HNO₃ (ACC-HNO₃) had the highest capacity for adsorption of DBT. Kinetic characterization of the adsorption process indicated that the mixed-order and modified pseudo-n-order models can describe the kinetics of adsorption of thiophenic compounds onto ACCs. The ACC and ACC-HNO₃ were used to test the removal efficiency of total sulfur contents (BT, DBT and DMDBT, 150 ppmw for each of them), too. The effect of shaking and ultrasound methods and also temperature and time on the regeneration of saturated ACC-HNO₃ with DBT was studied.     

Adsorption of zinc, cadmium and mercury ions from aqueous solutions on an activated carbon cloth

The adsorption of zinc, cadmium and mercury ions from aqueous solutions on an activated carbon cloth was studied as a function of their concentrations and solution pH. For that purpose, pertinent adsorption isotherm data was collected at different pH values. The amount of adsorbed zinc and cadmium ions increases while the amount of adsorbed mercury remains constant with an increase in the equilibrium pH of the solution. The adsorption mechanisms of metal ions on activated carbon cloth are discussed. Under the conditions investigated, these primarily involve adsorption of monovalent cations (Zn and Cd) or precipitation of metal hydroxides (Cd and Hg) on the activated carbon cloth tested.     

VOLATILE ORGANIC COMPOUND (VOC) REMOVAL BY ADSORPTION ONTO ACTIVATED CARBON FIBER CLOTH AND ELECTROTHERMAL DESORPTION: AN INDUSTRIAL APPLICATION

Previous studies have shown good adsorption of volatile organic compounds (VOC) present in air onto activated carbon fiber cloths (ACFCs). In a chemical plant, a treatment process was carried out to control a gaseous emission (flow close to 100 m³ h^-1) loaded with methylene chloride at concentrations ranging between 3 and 30 g m^-3. A final mass flow lower than 100 g h^-1 was required in the outlet emission. Two identical cylindrical ACFC modules worked alternately in an adsorption-desorption cycle. The outlet pollutant mass flow was found to be less than 4 g h^-1. After saturation of the adsorbent, the module was electrothermally regenerated. Desorbed methylene chloride was recovered in a cryogenic trap and reused in the chemical processes of the plant. This system worked continuously for more than 18 months (24 h per day) with no operating problems and giving good performance in terms of VOC outlet emission concentrations.     

Effect of surface acid groups associated with amorphous and structured carbon on the catalytic hydrodechlorination of chlorobenzenes

BACKGROUND: Catalytic hydrodechlorination (HDC) is a progressive approach to treating chlorinated waste streams. While carbon is widely used as a catalyst support, the influence of carbon surface functionality on HDC performance has not been established. This work sets out to assess the impact of surface acid groups associated with activated carbon (AC), graphite and graphitic nanofibers (GNF) on Pd promoted gas phase HDC of chlorobenzene (CB) and 1,3‐dichlorobenzene (DCB). RESULTS: The acid groups were introduced by HNO₃ washing and the HDC reaction performed over bulk Pd and Pd physically mixed with each carbon. The carbon was subjected to a thermal treatment to remove the surface acidity. Characterization was by temperature programmed decomposition (TPD), temperature programmed hydrogen treatment (TPH), BET area, acid‐base titration, scanning and transmission electron microscopy. TPD, TPH and titration analyses served to establish the presence of surface oxygen groups after acid washing and facilitated an evaluation of the effectiveness of the thermal treatment to remove these groups. CONCLUSIONS: The surface acid groups inhibited HDC activity, a response most pronounced for Pd + AC, less so for Pd + graphite, while the effect was slight for Pd + GNF. HDC inhibition is attributed to chloroarene interaction with the surface functional (notably carboxylic) groups that impedes HDC. Fractional dechlorination of DCB was equivalent to or lower than CB HDC; there is some evidence of DCB interactions with heat treated graphite and GNF that served to raise HDC activity. Effective HDC over carbon based catalysts requires removal of surface acid groups. Copyright © 2008 Society of Chemical Industry     

Production of activated carbon cloth with controlled structure and porosity from a new precursor

The production of micro and mesoporous activated carbon cloth (ACC) from commercial acrylic textile fibres by physical activation with carbon dioxide and the addition of boric acid and sodium hydrogen phosphate as impregnants is reported. The use of sodium hydrogen phosphate leads to samples with greater mesopore volume whereas other ACC production conditions studied mainly result in microporous materials. This work demonstrates that it is possible to produce carbon materials from a commercial acrylic textile cloth with the maintenance of the precursor shape, as shown by scanning electron microscopy (SEM). The materials are formed from layers of aromatic sheets that in a nanoscale resemble graphite and X-ray diffraction studies indicate microcrystallites with dimensions between 5.9 and 7.6 nm for L _a (width) and between 2.4 and 2.7 nm for L _c (height), corresponding to 7 to 8 parallel graphene layers.