Understanding the Role of Coordinatively Unsaturated Al³⁺ Sites on Nanoshaped Al₂O₃ for Creating Uniform Ni–Cu Alloys for Selective Hydrogenation of Acetylene

Abstract

In this work, we report a synthesis approach for catalyst preparation using shape-controlled Al2O3 supports with enriched quantities of coordinatively unsaturated Al3+ centers. These centers can then induce ordering in bimetallic catalysts, even with a simple impregnation strategy and this is shown to be beneficial for selective hydrogenation of acetylene. Interestingly, nanorod Al2O3 induced a highly homogeneous and ordered Ni1Cu1 nanoalloy, mainly attributed to the coordination effect of unsaturated Al3+ sites that accelerate atomic diffusion and ordering (affirmed by molecular simulation). The as-obtained Ni–Cu/Al2O3-rod catalyst exhibited both satisfactory activity and ethylene selectivity of 86% under mild reaction conditions, which outperformed most of Ni-based catalysts reported to date. Through the combination of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies and computational modeling by density functional theory, it was found that a di-σ-adsorption mode of acetylene on the ordered Ni1Cu1 nanoalloy featuring alternating rows of Cu and Ni atoms played a key role in the improvement of selectivity.

Electronic and Steric Modification of Ni Nanoparticle Surface via N-Doped Carbon Layers Enables Highly Selective Semihydrogenation of Alkynes

“…However, they generally showed inferior activity, lower selectivity to alkenes, and poor stability. To address these issues, diverse strategies have been innovated, including alloying with other metals to form intermetallics, surface and interfacial engineering, and confinement in porous supports, to precisely tuning the geometric and electronic structures of Ni NPs. − Consequently, the H 2 dissociation ability, adsorption/desorption strength, and configuration of alkynes and alkenes could be effectively regulated, thereby endowing with a substantial improvement in the reactivity, selectivity, and stability.…”

In Situ DRIFTS Analysis during Hydrogenation of 1‐Pentyne and Olefin Purification with Ag Nanoparticles

“…[1,11] On the other hand, other elements such as Ni, Ag, W, Cu, Fe, Cr, Co and their oxides can be used, as they are active and cheaper. [5,[12][13][14][15][16][17] Silver has a low affinity towards hydrogen due to the filled d-band (d 10 ), as opposed to metals such as nickel, palladium, and platinum (d 8 ). [18,19] Thus, the weak interaction of hydrogen with its extended metal surfaces such as those found in single crystals and polycrystalline surfaces, provides minimal dissociative chemisorption.…”

“…The most widely used heterogeneous catalysts are noble metals, such as Pt, Pd, Ru, Rh, which generally have higher activity and selectivity, but their cost is high [1,11] . On the other hand, other elements such as Ni, Ag, W, Cu, Fe, Cr, Co and their oxides can be used, as they are active and cheaper [5,12–17] …”

“…On the other hand, in the last decade Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) has become a very popular method for the characterization of catalysts and it has been applied quite extensively to the identification of all adsorbed species on the surface, and consequently can contribute to the identification of reaction intermediates [28] . Recent works of catalytic systems using infrared spectroscopy to study the adsorption of alkynes and alkenes over supported metal catalysts and single crystals, have been published [14,16,29–34] …”

“…[28] Recent works of catalytic systems using infrared spectroscopy to study the adsorption of alkynes and alkenes over supported metal catalysts and single crystals, have been published. [14,16,[29][30][31][32][33][34] There are very few researches over the use of heterogeneous Ag catalysts during the selective hydrogenation of pure alkynes at mild operational conditions, neither regarded the purification or alkene/alkyne mixtures. Besides, to optimize the performance of Ag catalysts, it is essential to understand the effect of the support over the catalytic activity during the selective hydrogenation processes.…”