Abstract
The inner surface of a metallic tube (i.d. 0.5 mm) was coated with a palladium (Pd)-based thin metallic layer by flow electroless plating. Simultaneous plating of Pd and silver (Ag) from their electroless-plating solution produced a mixed distributed bimetallic layer. Preferential acid leaching of Ag from the Pd–Ag layer produced a porous Pd surface. Hydrogenation of p-nitrophenol was examined in the presence of formic acid simply by passing the reaction solution through the catalytic tubular reactors. p-Aminophenol was the sole product of hydrogenation. No side reaction occurred. Reaction conversion with respect to p-nitrophenol was dependent on the catalyst layer type, the temperature, pH, amount of formic acid, and the residence time. A porous and oxidized Pd (PdO) surface gave the best reaction conversion among the catalytic reactors examined. p-Nitrophenol was converted quantitatively to p-aminophenol within 15 s of residence time in the porous PdO reactor at 40 °C. Evolution of carbon dioxide (CO2) was observed during the reaction, although hydrogen (H2) was not found in the gas phase. Dehydrogenation of formic acid did not occur to any practical degree in the absence of p-nitrophenol. Consequently, the nitro group was reduced via hydrogen transfer from formic acid to p-nitrophenol and not by hydrogen generated by dehydrogenation of formic acid.
Highlights
The flow reaction process enables continuous material production by feeding the reactants into one end of the reactor and obtaining the products from the other end [1,2,3,4,5,6,7,8,9]
scanning electron microscopy (SEM) and EDX analysis of the plated layer indicated the mixed distribution of Pd and Ag over the inner surface (Figure 1b)
Hydrogenation of 0.01 M p-nitrophenol with 0.1 M formic acid was conducted in aqueous solution at 30 °C and 40 °C by using tubular reactors coated with Pd, porous Pd, metallic Pd–Ag and porous PdO
Summary
The flow reaction process enables continuous material production by feeding the reactants into one end of the reactor and obtaining the products from the other end [1,2,3,4,5,6,7,8,9]. We developed catalytic tubular reactors of less than 0.5 mm inner diameter, of which the interior surfaces were coated uniformly with thin (1–2 μm) palladium (Pd), platinum (Pt), and rhodium (Rh) layers by an electroless plating procedure [10,11]. We have studied flow reactions, including the decomposition of hydrogen peroxide, oxidation of organic dyes, carbon–carbon coupling, and conversion of formic acid to hydrogen (H2) and carbon dioxide (CO2), using catalytic tubular reactors [10,11,12,13].
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