Liquid phase hydrodechlorination of chlorophenols over Pd/C and Pd/Al2O3: a consideration of HCl/catalyst interactions and solution pH effects
Liquid phase hydrodechlorination of chlorophenols over Pd/C and Pd/Al2O3: a consideration of HCl/catalyst interactions and solution pH effects
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DOI：
10.1016/j.apcatb.2004.04.015
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发表时间：
2004-10
影响因子：
22.1
通讯作者：
Guang Yuan;M. Keane
中科院分区：
文献类型：
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作者：
Guang Yuan;M. Keane
研究了2-氯苯酚（2-CP）和2，4-二氯苯酚（2，4-DCP）在1%（w/w）Pd/C和Pd/Al_2O_3催化剂上的液相加氢脱氯反应。2，4-DCP的HDC生成HCl和2-CP作为唯一的中间体部分脱氯产物，其进一步反应生成苯酚;在完全脱氯之前，在Pd/Al 2 O3上形成环己酮，但在Pd/C上不形成环己酮。Pd/Al 2 O3的特征在于（基于TEM分析）较小Pd颗粒的窄分布，得到表面积加权平均粒径= 2.4nm，其明显低于Pd/C确定的值13.2nm，其中后者的特征在于较大（球形）颗粒的更宽分布。NaOH的加入通过抑制由于生成的HCl引起的HDC抑制来增加脱氯分数。重复使用的催化剂显示了明显的失活Pd/C和有限的损失的活性的情况下，Pd/Al 2 O3。Pd/C的失活可能与减少有关（高达约60%）的初始BET表面积与可观的浸出（高达约。40%）的起始Pd含量，并且虽然平均Pd直径基本上不受影响，但有证据表明较大Pd颗粒的优选浸出。Pd/Al 2 O3中普遍存在的较强的金属/载体相互作用导致在有/无NaOH添加的催化剂重复使用期间有限的Pd浸出和相当的初始HDC活性。在反应混合物（pH 5-1.5）中加入HCl导致与Pd/Al 2 O3相关的初始HDC速率显著下降，而Pd/C的HDC活性下降较小。响应于本体溶液pH值的变化的差异进行了讨论，在溶液中的活性物种的性质和两性行为的Pd支持。
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/Al2O3under 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/Al2O3is characterized (on the basis of TEM analysis) by a narrow distribution of smaller Pd particles to give a surface area weighted mean particle diameter = 2.4nm that is appreciably lower than the value of 13.2nm 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/Al2O3results 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/Al2O3and 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.