Supported CuO/γ-Al2O3 as heterogeneous catalyst for synthesis of diaryl ether under ligand-free conditions

CuO/γ-Al2O3 was employed as catalyst in the coupling reaction of iodobenzene with m-cresol to give 3-methyldiphenyl ether under ligand-free conditions. It performed more efficiently than other supported CuO catalysts (CuO/SBA-15, CuO/ZrO2, CuO/CeO2, CuO/La2O3). Reaction conditions were investigated and the yield reached 76% under the optimized terms. As a heterogeneous catalyst, CuO/γ-Al2O3 could be reused for three cycles with moderate to good yields. According to the results of XRD, TPR and XPS, the catalytic activities of supported CuO catalysts were due to the highly dispersed Cu(II) species and independent of the electronic state of these copper species.

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► Supported CuO/γ-Al2O3 was effective for Ullmann reaction under ligand-free conditions.
► CuO/γ-Al2O3 could be reused for at least three times.
► Cu2+ or CuO was the main active species in heterogeneous Ullmann reaction.
► Highly dispersed copper species showed higher catalytic activity than bulk ones.