Heterogeneous PdAg alloy catalyst for selective methylation of aromatic amines with formic acid under an additive-free and solvothermal one-pot condition

Abstract

The methylation of amines for the synthesis of methylamines and dimethylamines as platform chemicals has been attempted mostly by homogeneous catalysts with acid additives. However, there are scarcely any reports on heterogeneous catalytic methylation reactions except for a routine approach under high temperature and high pressure of CO 2 and H 2 gases for extended reaction times. Here we report a heterogeneously catalyzed selective methylation of aromatic amines using reactive and nontoxic formic acid as the only source for the construction of methyl groups, under ambient pressure in an additive-free one-pot reaction condition. Equal proportions of Pd and Ag in the PdAg/Fe 3 O 4 /N-rGO catalyst deliver highly selective amine methylation without aromatic ring hydrogenation, as the strained Pd in the alloy is combined with the graphene-derived support, preventing nanoparticle agglomeration and the action of magnetite as a promoter. Both N-methylation and N,N-dimethylation of various substituted aromatic amines were performed with complete conversion and excellent 90-97% selectivity by controlling the reaction times in the range of 10-24 h at 140°C without unwanted aromatic ring hydrogenation. Furthermore, the developed bimetallic catalyst provided high yields (88-91%) of methylation with CO 2 +H 2 gas under high pressure, which are as good as the results of homogenous catalysts with an acid additive. To the best of our knowledge, our use of this environmentally friendly methodology is the first time that this durable heterogeneous catalyst has readily performed highly selective methylation at ambient pressure, which is attractive for industrial applications.

Au@PdAg core–shell nanotubes as advanced electrocatalysts for methanol electrooxidation in alkaline media

“…1f) that is consistent with that of the (111) planes of fcc Au (0.235 nm), 40 and the other with an interplanar spacing of 0.230 nm and 0.199 nm (Fig. 1g), which are between the lattice spacing of (111) and (002) planes of pure Ag and pure Pd, 40,41 indicating the formation of PdAg alloy. The formation of PdAg alloy can also be conrmed by XPS analysis (Fig.…”

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“…5b, L2) as privileged ligands in combination with a ruthenium or cobalt precursor. Notable developments from 2015 to 2019 reached in the field of heterogeneous catalysis were described by the groups of Kim 146 148 respectively, were showcased as active systems.…”

Microbial synthesis of graphene‐supported highly‐dispersed Pd‐Ag bimetallic nanoparticles and its catalytic activity

“…(C), right panel) attributed to metallic Pd, and the peaks at 368.2 and 374.2 eV (inset in Fig. (C), left panel) ascribed to 3d 5/2 and 3d 3/2 of Ag, respectively . Therefore, the Pd(II) and Ag(I) were reduced during the reduction by S. oneidensis MR‐1.…”

“…4(C), left panel) ascribed to 3d 5/2 and 3d 3/2 of Ag, respectively. 28 Therefore, the Pd(II) and Ag(I) were reduced during the reduction by S. oneidensis MR-1. The reduction of GO was also monitored by FTIR spectroscopy and Raman spectroscopy.…”