Selective hydrogenation of nitrostyrene to aminostyrene over Pt/TiO2 catalysts: Effects of pressurized carbon dioxide and catalyst preparation conditions

Abstract

The present work has studied the influence of CO 2 pressurization on the hydrogenation of nitrostyrene (NS) using Pt/TiO 2 . With CO 2 pressurization up to 12 MPa (CO 2 -dissolved expanded liquid (CXL) phase), the over-all reaction rate and the selectivity to aminostyrene (AS) increased. At higher CO 2 pressures where all NB dissolved in scCO 2 (scCO 2 -homogeneous phase), both of them decreased with increasing the CO 2 pressure. The phase behavior was an important factor for the present reaction system. It was also found that the presence of pressurized CO 2 gave higher selectivity to AS than in its absence at any conversion level. This was ascribed to retardation effects of dense phase CO 2 on the hydrogenation of AS to ethylaniline. Competitive adsorption of nitro and vinyl groups was suggested to determine the product selectivity. FTIR measurements showed that the pressurized CO 2 lowers the reactivity of the nitro group, and this effect is stronger in scCO 2 -homogeneous phase than in CXL phase, resulting in the lower AS selectivity in the former phase. Lower Pt loadings and higher catalyst reduction temperatures gave Pt/TiO 2 catalysts more selective for the AS formation. FTIR measurements of adsorbed CO over the catalysts suggested that the presence of less-coordinated Pt atoms on edge, corner and kink sites was significant for the selective hydrogenation of NS to AS.

A multiphase reaction medium including pressurized carbon dioxide and water for selective hydrogenation of benzonitrile with a Pd/Al2O3 catalyst

“…Similar FTIR measurements were made for liquid BN dissolving CO 2 at high pressures by ATR mode [31]. Fig.…”

“…In situ high-pressure FTIR was used to examine the interactions between CO 2 and BN molecules in the absence and presence of water using a JASCO FTIR-620 spectrometer with a triglycine sulfate detector at a frequency resolution of 2 cm -1 . The FTIR measurements were made with a home-designed high pressure cell of 1.18 cm 3 attached with a ZnSe rod in attenuated total reflection (ATR) mode [31]. A certain volume of BN was introduced into the cell and it was purged with CO 2 several times.…”

“…Carbon dioxide molecules are dissolved in organic liquids at high pressures and may interact with chemical species in these phases [9,30,31,35]. For example, CO 2 molecules interact with carbonyl group of cinnamaldehyde [35] and nitro group of nitrobenzene [9], as evidenced by in situ high-pressure FTIR measurements for the organic compounds dissolved in pressurized CO 2 .…”

Flame-made Pt/TiO2 catalysts for the liquid-phase selective hydrogenation of 3-nitrostyrene

“…Functionalized anilines are industrially important intermediates for pharmaceuticals, polymers, herbicides, and other substances and fine chemicals [1][2][3]. The selective reduction of a nitro group when other reducible groups are present in the same molecule is very challenging.…”

“…Fujita et al [2] used pressurized CO 2 as the reaction medium and found that higher selectivity to VA was obtained than in its absence at any conversion level. The effect of dense-phase CO 2 was ascribed to retardation on the hydrogenation of vinylaniline (VA) to ethylaniline (EA).…”