کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
149362 456431 2012 11 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
The role of hydrogen partial pressure in the gas phase hydrogenation of p-chloronitrobenzene over alumina supported Au and Pd: A consideration of reaction thermodynamics and kinetics
موضوعات مرتبط
مهندسی و علوم پایه مهندسی شیمی مهندسی شیمی (عمومی)
پیش نمایش صفحه اول مقاله
The role of hydrogen partial pressure in the gas phase hydrogenation of p-chloronitrobenzene over alumina supported Au and Pd: A consideration of reaction thermodynamics and kinetics
چکیده انگلیسی

The gas phase hydrogenation of p-chloronitrobenzene (p-CNB) over alumina supported Au and Pd has been subjected to thermodynamic and kinetic analyses where the H2 partial pressure was varied from excess (H2/p-CNB up to 2300) to lean (stoichiometric) conditions. The catalysts have been characterised by temperature-programmed reduction (TPR), H2 chemisorption/temperature-programmed desorption (TPD), BET surface area/porosity, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) measurements. Both catalysts exhibited nano-scale metal particles (mean diameter = 4.5 nm (Au) and 2.4 nm (Pd)) with the formation (from XPS analysis) of electron-rich Pdδ− but no significant electron transfer between Au and Al2O3. Under thermodynamic control, cyclohexane is the only product where H2/p-CNB ⩾ 10 with product (p-chloroaniline, aniline, chlorobenzene, benzene and cyclohexane) dependence on H2/p-CNB in the range 1–8; at a given H2/p-CNB, reaction temperature (373–473 K) has a negligible effect. Under conditions of catalytic control, Au/Al2O3 generated p-chloroaniline as the sole product while Pd/Al2O3 promoted hydrodechlorination to nitrobenzene and hydrogenation to aniline. A kinetic model is presented that accounts for the rate dependence on H2 partial pressure, where the maximum turnover frequency delivered by Au/Al2O3 (with a lower H2 adsorption coefficient) was an order magnitude lower than that recorded for Pd/Al2O3. Adsorption of p-CNB on Pdδ−via the aromatic ring is proposed that serves to activate both –NO2 and –Cl for attack whereas Au/Al2O3 selectively activates –NO2, leading to exclusive production of p-chloroaniline.

Figure optionsDownload as PowerPoint slideHighlights
► First reported thermodynamic/kinetic analysis of p-chloronitrobenzene hydrogenation.
► Selective –NO2 reduction over Au/Al2O3 from excess H2 to stoichiometric conditions.
► Pd/Al2O3 activates –NO2 and –Cl, promoting hydrogenation/hydrodechlorination.
► Coupling of Au/Al2O3 and Pd/Al2O3 surface characteristics with performance.
► Kinetic model that accounts for rate dependence on H2 partial pressure.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Chemical Engineering Journal - Volume 210, 1 November 2012, Pages 103–113
نویسندگان
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