Preparation of Mesoporous Ni–alumina Catalyst by One-step Sol–gel Method: Control of Textural Properties and Catalytic Application to the Hydrodechlorination of o-dichlorobenzene

Mesoporous Ni–alumina catalysts (Ni–alumina-pre and Ni–alumina-post) were synthesized by one-step sol–gel method using micelle complex comprising lauric acid and nickel ion as a template with metal source and using aluminum sec-butoxide as an aluminum source. The Ni–alumina catalysts showed relatively high surface areas (303 m²/g for Ni–alumina-pre and 331 m²/g for Ni–alumina-post) and narrow pore size distributions centered at ca. 4 nm. Highly dispersed Ni particles were observed in the Ni–alumina catalysts (ca. 5.2 nm for Ni–alumina-pre and ca. 6.8 nm for Ni–alumina-post) after reduction at 550 °C, while a catalyst prepared without a template (NiAl-comp) exhibited inferior porosity with large metal particles (ca. 12.3 nm). Mesoporous Ni–alumina catalysts with different porosity were obtained by employing different hydrolysis step of aluminum source. When aluminum source was hydrolyzed under the presence of micelle complex, a supported Ni catalyst with highly developed framework mesoporosity was obtained (Ni–alumina-post). On the other hand, when aluminum source was pre-hydrolyzed followed by mixing with micelle solution, the resulting catalyst (Ni–alumina-pre) retained high portion of textural porosity. It was revealed that the hydrolysis method employed in this research affected not only textural properties but also metal-support interaction in the Ni–alumina catalysts. It was also found that the Ni–alumina-pre catalyst exhibited weaker interaction between nickel and alumina than the Ni–alumina-post, leading to higher degree of reduction in the Ni–alumina-pre catalyst. In the hydrodechlorination of o-dichlorobenzene, the Ni–alumina catalysts exhibited better catalytic performance than the NiAl-comp catalyst, which was attributed to higher metal dispersion in the Ni–alumina catalysts. In particular, the Ni–alumina-pre catalyst showing 1.5 times higher degree of reduction and larger amounts of o-dichlorobenzene adsorption exhibited better catalytic performance than the Ni–alumina-post catalyst.     

Catalytic hydrodechlorination of 1-chlorooctadecane, 9,10-dichlorostearic acid, and 12,14-dichlorodehydroabietic acid in supercritical carbon dioxide

Kinetic and thermodynamic analyses of catalytic hydrodechlorinations in supercritical carbon dioxide (SC-CO₂) were performed using 5% Pd supported on γ-Al₂O₃. The selected standard compounds used for the study represented chlorinated wood resins commonly found in pitch deposits; 1-chlorooctadecane (C₁₈-Cl), 9,10-dichlorostearic acid (Stearic-Cl₂), and 12,14-dichlorodehydroabietic acid (DHA-Cl₂). The reaction utilized isopropanol as a hydrogen donor. Pressure, temperature, and the concentrations of isopropanol and palladium were varied to study the effect of each parameter and to optimize the dechlorination yield. The reaction in SC-CO₂ was compared to the one in liquid solvents at atmospheric pressure. By applying a Langmuir–Hinshelwood kinetic model, the rate-determining step of the reaction was deduced to be adsorption of the chlorinated molecules on the palladium surface. The apparent activation energies of the reactions for C₁₈-Cl, Stearic-Cl₂, DHA-Cl₂ were 43±5, 40±7, and 135±7 kJ mol⁻¹, respectively, in SC-CO₂. The relatively high activation energy for DHA-Cl₂ was apparently due to structural differences from the other two compounds. The apparent activation energy of dechlorination of C₁₈-Cl in liquid isopropanol at atmospheric pressure was determined to be 35±3 kJ mol⁻¹, leading to the conclusion that the rate-determining step is the same for this compound in both fluid systems. The enthalpies of desorption of stearic acid and dehydroabietic acid were determined to be 18±2 and 12±2 kJ mol⁻¹, respectively. These values being less than half of the apparent activation energies of dechlorination of their corresponding chlorinated compounds indicates that desorption of the dechlorinated products is not the rate-determining step of the reaction. This was consistent with the conclusion that the rate-determining step is adsorption, on the understanding that the reaction mechanism is same in both fluid systems.     

α-丙二醇-水相中氯代二噁英的催化加氢脱氯降解

二噁英类物质由于具有亲脂性、高毒性、化学结构稳定、难生物降解而在环境中持久存在,成为持久性有机污染物的典型代表.二嗯英的去除方法研究,一直是国际研究的热点.以5％钯/炭为催化剂,氢气作为氢源,以环境友好的α-丙二醇-水为溶剂,在1 mol/L氢氧化钠的碱性条件下,研究了1,2,7,8-四氯代二噁英（1,2,7,8-TCDD）的催化加氢脱氯降解.探讨了反应温度、初始浓度、反应时间、催化剂用量等对1,2,7,8-TCDD去除率的影响.结果表明,在反应初期（前5 min）,反应速率较快;在反应温度为45℃,催化剂用量为0.5 g/mL,反应时间为150 min的条件下,1,2,7,8-TCDD的去除率达97.0％;初始浓度对1,2,7,8-TCDD的去除率没有影响.初步试验结果表明,催化加氢脱氯降解是去除环境中氯代二嗯英的有效手段,但实际应用还有待于进一步研究.     

Liquid phase hydrodechlorination of chlorophenols over Pd/C and Pd/Al2O3: a consideration of HCl/catalyst interactions and solution pH effects

The liquid phase hydrodechlorination (HDC) of 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP) has been studied over 1% (w/w) Pd/C and Pd/Al₂O₃ under conditions of minimal mass transport constraints. The HDC of 2,4-DCP generated HCl and 2-CP as the only intermediate partially dechlorinated product which reacts further to yield phenol; cyclohexanone was formed over Pd/Al₂O₃, but not over Pd/C, prior to complete dechlorination. Pd/Al₂O₃ is characterized (on the basis of TEM analysis) by a narrow distribution of smaller Pd particles to give a surface area weighted mean particle DIAMETER = 2.4 nm that is appreciably lower than the value of 13.2 nm established for Pd/C, where the latter is characterized by a broader distribution of larger (spherical) particles. The addition of NaOH served to increase fractional dechlorination by suppressing HDC inhibition due to the HCl that is generated. Reuse of the catalysts revealed an appreciable deactivation of Pd/C and a limited loss of activity in the case of Pd/Al₂O₃. Deactivation of Pd/C can be linked to a decrease (up to ca. 60%) in the initial BET surface area allied to appreciable leaching (up to ca. 40%) of the starting Pd content through the corrosive action of HCl and, while the average Pd diameter is essentially unaffected, there is evidence of a preferred leaching of larger Pd particles. The stronger metal/support interactions prevalent in Pd/Al₂O₃ results in limited Pd leaching and comparable initial HDC activities during catalyst reuse with/without NaOH addition. Inclusion of HCl in the reaction mixture (pH 5–1.5) resulted in a marked decline in the initial HDC rate associated with Pd/Al₂O₃ and a lesser drop in HDC activity for Pd/C. The difference in response to bulk solution pH variations are discussed in terms of the nature of the reactive species in solution and the amphoteric behavior of the Pd supports.     

Preparation of Benzylamine by Highly Selective Reductive Amination of Benzaldehyde Over Ru on an Acidic Activated Carbon Support as the Catalyst

Platinum particles (<1.5 nm) have been shown to behave as bases in their interaction with -alumina. FTIR spectra of adsorbed pyridine probe molecules showed that the acid strength of the -alumina was decreased by the presence of (<1.5 nm) Pt particles. Ammonium chloride treatment converts the primary Pt clusters to H _x Pt _y Cl _z intermediates that de-anchor from the support. Consequently, agglomeration to 8 nm Pt particles was observed following treatment in hydrogen at a relatively mild temperature. For the treated catalyst the IR data of absorbed pyridine show a 3 cm^-1 increase relative to the original Pt/-Al₂O₃ catalyst, indicating a strengthening of the acidity. Changes in the Pt particle size were confirmed by FTIR spectroscopy of CO absorbed onto the Pt particles before and after treatment. Consecutive CO and pyridine probe adsorption demonstrated the electronic interplay between the Pt particles and the support. Pyridine adsorption onto the -alumina support of a Pt/Al₂O₃ catalyst pre-dosed with CO produces a nearly 40 cm^-1 lowering of the CO peak position, indicative of CO bond weakening. In the case of CO adsorbed onto a catalyst pre-dosed with pyridine, a shift in the pyridine IR spectrum was only observed from the original highly dispersed catalyst.     

Gas-phase hydrodechlorination of pentachlorophenol over supported nickel catalysts

The gas-phase hydrodechlorination of pentachlorophenol (PCP) over nickel/silica and nickel/Y zeolite catalysts at 573 K has been studied. Each catalyst was 100% selective in cleaving the C–Cl bonds, leaving the hydroxyl substituent and benzene ring intact. The variation of catalytic activity and selectivity (in terms of partial and full dechlorination) with time-on-stream is illustrated and catalyst deactivation is addressed. Dechlorination efficiency is quantified in terms of dechlorination rate constants, phenol selectivity/yield and the ultimate partitioning of chlorine in the parent organic and product inorganic host. Increasing the nickel loading on silica was found to raise the overall level of dechlorination while the use of a zeolite support introduced spatial constraints that severely limited the extent of dechlorination. Product composition was largely determined by steric effects where resonance stabilisation had little effect. The reaction pathways, with associated pseudo-first-order rate constants, are also presented. This revised version was published online in November 2006 with corrections to the Cover Date.     

二氯乙酸选择性加氢脱氯制备高纯氯乙酸

以Pd/C为催化剂,通过固定床反应器对含氯乙酸、二氯乙酸以及乙酸的氯化液进行选择性催化加氢脱氯研究,使氯化液中的大部分或全部二氯乙酸转化为一氯乙酸或乙酸。考察催化剂制备条件对催化性能的影响,结果表明,在Pd负载质量分数0.9%、浸渍液浓度4.5 g·L-1和浸渍温度20℃条件下制备的催化剂,催化活性和产物选择性最佳,运行时间超过1 500 h活性未出现明显衰减。     

KMg1?xPdxF3 with Perovskite-Like Structures as Precursors for the Catalytic Hydroconversion of CCl2F2 and CHClF2

Several fluoride type perovskites, with formula KMg_1–x Pd _x F₃, have been prepared for the first time. The enlargement of their cell parameters has been associated with the insertion of Pd into the structure. After reduction, these new compounds, when tested in the hydrodechlorination reaction of CCl₂F₂ and CHClF₂, showed higher selectivities to CHClF₂ and CH₂F₂, respectively, than other Pd catalysts supported on KMgF₃.     

Effect of Ni loading and calcination temperature on catalyst performance and catalyst deactivation of Ni/SiO2 in the hydrodechlorination of 1,2‐dichloropropane into propylene

The hydrodechlorination of 1,2‐dichloropropane (DCPA), a chlorinated organic waste which is produced in the epichlorohydrin process, to propylene was carried out over Ni/SiO₂ catalysts. The effects of Ni loading and calcination temperature on catalyst performance and catalyst deactivation of Ni/SiO₂ were systematically investigated. The Ni/SiO₂ catalysts efficiently converted DCPA into propylene in 95% selectivity or higher. The particle size of Ni on SiO₂ was strongly related to the catalyst stability. In terms of the effect of Ni loading, the largest Ni particles on SiO₂ showed the best durability against deactivation. A series of TPR and UV‐DRS measurements revealed that nickel hydrosilicate was formed as the result of the interaction between Ni and SiO₂. Nickel hydrosilicate was found to be responsible for the catalyst stability leading to low catalyst deactivation. HCl adsorption on Ni/SiO₂ was the main reason for catalyst deactivation. HCl modified the crystal structure of metallic Ni to NiCl₂ and led to irreversible deactivation and metal sintering. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pd/C纳米结构的尺寸调控及液相高效加氢脱氯性能

在甲酰胺体系下,利用KBr调控合成了Pd粒径为2 nm、3 nm、4 nm和6 nm的不同水溶性Pd/C催化剂,采用TEM、XRD和XPS对催化剂进行表征,并以4-氯苯酚为反应物,测试了催化剂的液相加氢脱氯性能。结果表明,相比于商业Pd/C催化剂,在甲酰胺体系中合成的Pd/C催化剂具有更高的水溶性,催化效果提高了约40%以上。同时研究了不同溶剂对催化剂加氢脱氯效果的影响,结果表明,随着溶液极性、溶剂的介电常数(ε)、偶极矩(μ)和归一化极性参数(ETN)的增强,催化效果越好。