Iron Oxide as a Catalyst for Nitroarene Hydrogenation: Important Role of Oxygen Vacancies

Abstract

Heterogeneous catalytic hydrogenation of nitroarenes is one of the most important chemical transformations, and exploring earth-abundant catalysts is very attractive for application. Herein, we studied the catalytic activity of several iron oxide catalysts with similar structure and surface area. It is found that γ-Fe 2 O 3 , α-Fe 2 O 3 , and FeO show obvious but a little limited activity, but the activity of the used catalyst is increased in the second run, especially for γ-Fe 2 O 3 . Characterization shows that Fe 2 O 3 is partly reduced with many oxygen vacancies produced on the surface, which accounts for the high hydrogenation activity. Finally, Fe 3 O 4 exhibits activity significantly higher than Fe 2 O 3 and FeO, and 100% selectivity in the hydrogenation of nitroarenes to anilines. Also, Fe 3 O 4 is easy to separate by a magnetic field and shows excellent recycling stability.

Phosphorus‐Doped and Lattice‐Defective Carbon as Metal‐like Catalyst for the Selective Hydrogenation of Nitroarenes

“…Noble metals (especially palladium and platinum) and their alloys have been utilized to activate H 2 molecules under moderate conditions and facilitate subsequent hydrogenation of the −NO 2 group by dissociated H atoms because they are abundant of delocalized electrons and can afford suitable interaction with H 2 and the nitro group, but their high costs and rare reserves limit their large‐scale application. Recently, non‐noble metal‐oxide based catalysts, for instance, nanoscale cobalt and iron oxide supported on a nitrogen‐doped carbon matrix, oxygen‐deficient tungsten oxide, and iron oxide were reported as potential catalysts for the selective hydrogenation of nitro aromatics. Nevertheless, there are still significant interests in inexpensive metal‐free catalysts for hydrogenation.…”

Enhancing Oxygen Storage Capability and Catalytic Activity of Lanthanum Oxysulfide (La2O2S) Nanocatalysts by Sodium and Iron/Sodium Doping

“…Figure S3 A and Figure S3 B (in the Supporting Information) present the TGA and correlated derivative weight by time (d wt /d t ) profile of Fe/Na co‐doped La 2 O 2 S. Based on these results, Table summarizes the V osc values, showing that if the iron doping ratio increased from zero to 0.06, the OSC value of La 2 O 2 S is three times higher for 0.06Fe/3Na/La 2 O 2 S ( V osc =1.9528 mmol O 2 /g cat ) than those for 0Fe/3Na/La 2 O 2 S ( V osc =0.6117 mmol O 2 /g cat ). We postulate that replacement of La 3+ with Fe 3+ ions, the oxygen vacancy generated by Na doping may reduce Fe 3+ to Fe 2+ ions, which can capture the oxygen from air through the redox Fe 2+ →Fe 3+ couple, consequently increasing the OSC of La 2 O 2 S . For 0.1Fe/3Na/La 2 O 2 S with increased iron doping ratio, the OSC value dropped rapidly to 0.488 mmol O 2 /g cat , which is lower than 0Fe/3Na/La 2 O 2 S ( V osc =0.611 mmol O 2 /g cat ), most likely owing to the formation of α‐Fe 2 O 3 , which can block active sulfur sites on the catalyst surface, consistent with the Raman spectra in Figure , which did not show any oxygen vacancy in bulk La 2 O 2 S.…”

“…The presence of a redox couple in catalysts, such as CeO 2 (Ce 4+ /Ce 3+ ), has been reported to increase OSC by Na doping . We hypothesized that introducing iron(III) ions together with sodium doping would create an iron redox couple (Fe 3+ →Fe 2+ ), which, in turn, increases OSC owing to oxidation of Fe 2+ . Figure shows the TEM images of the Fe/Na co‐doped La 2 O 2 S nanoparticles with 1.5 mmol Na(acac) and different iron doping ratios.…”

“…[18,19,21] We hypothesized that introducing iron(III) ions together with sodium doping would create an iron redox couple (Fe 3 + !Fe 2 + ), which, in turn, increases OSC owing to oxidation of Fe 2 + . [31][32][33] Figure 6s hows the TEM images of the Fe/Na co-doped La 2 O 2 Sn anoparticles with 1.5 mmol Na(acac)a nd differenti ron doping ratios. As the iron doping ratio increased, the morphologies changed from hexagonal nanoplates (0.02Fe/3Na/La 2 O 2 S) to nanowires (0.08Fe/ 3Na/La 2 O 2 Sa nd 0.1Fe/3Na/La 2 O 2 S).…”

“…+ ions, the oxygen vacancy generated by Na doping may reduce Fe 3 + to Fe 2 + ions, which can capture the oxygen from air through the redox Fe 2 + !Fe 3 + couple,c onsequently increasing the OSC of La 2 O 2 S [31][32][33]. For 0.1Fe/3Na/La 2 O 2 Sw ith increased iron dopingr atio, the OSC value dropped rapidlyt o 0.488 mmol O 2 /g cat ,w hich is lower than 0Fe/3Na/La 2 O 2 S( V osc = 0.611mmolO 2 /g cat ), most likely owing to the formation of a-Fe 2 O 3 ,w hich can block active sulfur sites on the catalysts urface, consistentw ith the Raman spectra in…”