INFLUENCE OF ALLOYING PLATINUM FOR THE HYDROGENATION OF PARA-CHLORONITROBENZENE OVER PTM/AL2O3 CATALYSTS WITH M = SN, PB, GE, AL, ZN
INFLUENCE OF ALLOYING PLATINUM FOR THE HYDROGENATION OF PARA-CHLORONITROBENZENE OVER PTM/AL2O3 CATALYSTS WITH M = SN, PB, GE, AL, ZN
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DOI：
10.1016/0304-5102(92)85022-8
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发表时间：
1992-02-01
影响因子：
--
通讯作者：
FIGUERAS, F
中科院分区：
文献类型：
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作者：
COQ, B;TIJANI, A;FIGUERAS, F
采用Pt/Al2O3和PtM/Al2O3催化剂（M = Sn, Pb, Ge, Al, Zn），研究了甲醇悬浮液中对氯硝基苯（CNB）在303 K和常压下的加氢反应。在分散良好的Pt/Al2O3母样品上，采用控制表面反应法制备了双金属催化剂。反应动力学遵循修正的Langmuir-Hinshelwood模型，CNB与氢之间存在竞争吸附。在高CNB浓度下，吸附竞争不再存在：在被CNB饱和的Pt表面，仍然有Pt位点可用于较小的氢分子的化学吸附。然后提出了一个速率定律，可以同时确定吸附常数和速率常数。在加入第二种金属M后，每个Pt表面原子的比活度在化学成分M/Pt相等时达到最大值，为0.1-0.2。结果表明，第二金属的缺电子物质通过激活氮-氧键来促进反应速率；离子锡是较好的促进剂。在高CNB转化率（> 98%）下，期望产物对氯苯胺（CAN）的收率从纯Pt/Al2O3的82%提高到PtSn/Al2O3 （Sn/Pt = 0.36）的97.5%。对CAN选择性的提高不是由于CAN脱卤速率的降低，不受合金化的影响。实际上，第二种金属的促进作用使CAN和CNB之间的相对吸附强度降低了10倍，然后CAN很容易被CNB从表面去除，从而阻止了加氢脱氯。
Hydrogenation of p-chloronitrobenzene (CNB) has been studied, in methanol suspension, at 303 K and atmospheric pressure, over a series of Pt/Al2O3 and PtM/Al2O3 catalysts (M = Sn, Pb, Ge, Al, Zn). The bimetallic catalysts were prepared by the so-called controlled surface reaction method by reacting organometallic compounds on the well-dispersed Pt/Al2O3 parent sample. The kinetics obeys a modified Langmuir-Hinshelwood model with competitive adsorption between CNB and hydrogen. The competition of adsorption no longer holds at high CNB concentration: on the Pt surface saturated by CNB, there are still Pt sites available for the chemisorption of the smaller hydrogen molecule. A rate law is then proposed which allows both adsorption and rate constants to be determined. Upon addition of the second metal M, the specific activity per Pt surface atom goes through a maximum value around a chemical composition M/Pt congruent-to 0.1-0.2. It is suggested that an electron-deficient species of the second metal promotes the reaction rate by activating the nitrogen-oxygen bond; ionic tin species are better promoters for this purpose. At high CNB conversion (> 98%) the yield of the desired product, p-chloroaniline (CAN), increases from 82% on pure Pt/Al2O3 to 97.5% on PtSn/Al2O3 (Sn/Pt = 0.36). The improvement of selectivity to CAN is not due to a decrease in CAN dehalogenation rate, which is not affected by alloying. Actually, the promoting effect of the second metal decreases the relative strength of adsorption between CAN and CNB up to a factor of 10: CAN is then easily removed from the surface by CNB, thus preventing hydrodechlorination.