Zirconium Modification Promotes Catalytic Activity of a Single-Site Cobalt Heterogeneous Catalyst for Propane Dehydrogenation

Abstract

The effect of Zr modification on the catalytic activity of Co/SiO 2 was investigated for nonoxidative propane dehydrogenation. Isolated Zr on SiO 2 surface sites were prepared by organometallic synthesis using Zr(O t Bu) 4 as a precursor. The resulting Zr/SiO 2 support was functionalized with Co 2+ ions via strong electrostatic adsorption. Spectroscopic (diffuse reflectance infrared Fourier transform spectroscopy, UV–vis, electron paramagnetic resonance) and microscopic characterization (transmission electron microscopy, scanning transition electron microscopy) results are consistent with single-site cobalt that preferentially associates with the mono-dispersed Zr at a variety of loadings and Co/Zr ratios. The oxidation state of Co in the as-prepared Co/SiO 2 and Co–Zr/SiO 2 was both +2 with tetrahedral and octahedral geometries, respectively. In situ X-ray absorption near edge structure and extended X-ray absorption fine structure results confirmed that the oxidation state of Co remained as +2 under reaction condition for both Co/SiO 2 and Co–Zr/SiO 2 samples and both catalysts have tetrahedral Co 2+ as the active catalyst. Despite similar Co coordination environments, the catalytic activity and selectivity was significantly improved by the Zr modification of the silica support versus Co/SiO 2 . This was attributed to the change in oxygen donor ability and Co–O bond strength of the ≡SiO–Zr–O sites of Co–Zr/SiO 2 compared with the ≡SiO– ligands in Co/SiO 2 . These results show that tuning of the support SiO 2 oxygen donation ability by use of an anchoring site (e.g., ≡SiO–Zr–O – ) can be used to alter both rate and selectivity of propane dehydrogenation with single-site heterogeneous catalysts. These results also show some preference for Co 2+ active sites to associate with ≡SiO–Zr–O – sites over ≡SiO–.

Effect of Zirconia on Hydrothermally Synthesized Co3O4/TiO2 Catalyst for NOx Reduction from Engine Emissions

“…The tuning of the support TiO 2 oxygen donation ability by use of an anchoring site (e.g., ≡TiO-Zr-O − ) can be used to alter both rate and selectivity of conversion efficiency i.e., (NO x , CO, HC). Possibly Co 2+ active sites prefer to associate with ≡TiO-Zr-O − sites as compare to ≡TiO- [42,43] as shown in below Figure 10. Furthermore, zirconia promoted catalyst efficiency is attributed by the presence of zirconia that effect on redox properties through dispersion of active phases which oxidize CO more efficiently.…”

“…Hydrocarbons conversion efficiency was noticed as 82.5% for simple catalyst at 1500 RPMs as shown in Figure 12 but in case of promoted catalyst HC Furthermore, the type of basic sites together with whole basicity and whole acidity of the ZrO2based catalysts also effect the HC, CO, and NOx conversion on active sites. The Lewis basic sites of ZrO2 consist of coordinately unsaturated O −2 species and the Lewis acidic sites is Zr 4+ species [42][43][44][45][46]. Overall reactions on the surface of catalysts were given below in Figure 11: Amin et al [39] developed a copper-based catalytic converter and reported that it converted HCs by 33% and CO by 66% at full load.…”

Cobalt‐Based Catalyst Supported on Different Morphologies of Alumina for Non‐oxidative Propane Dehydrogenation: Effect of Metal Support Interaction and Lewis Acidic Sites

“…[21] Co/Al 2 O 3 À NS and Co/Al 2 O 3 À NF samples shows higher intensities at the three positions whereas Co/Al 2 O 3 À NP shows lower intensity peaks with the broad band at 720 nm and 420 nm indicative of octahedral Co + 2 species. [23] The Co/ Al 2 O 3 À NS catalyst consists of Co + 2 mostly in the tetrahedral state, Co/Al 2 O 3 À NF consists of a mixture of Co + 2 in the tetrahedral and octahedral state, and Co/Al 2 O 3 À NP consists mostly of octahedral state originated from the Co 3 O 4 as a precursor with a small intensity of tetrahedral Co + 2 peaks.…”

“…[22] This analysis will help to generate a correlation between the activity, different coordination states of cobalt, and the distinctive role of tetrahedral and octahedral coordinated Co + 2 in dehydrogenation reaction. [23]…”

Atomic Layer Deposition for Preparing Isolated Co Sites on SiO2 for Ethane Dehydrogenation Catalysis

“…Their observation that selectivities increased with decreasing Co content suggested that the selective sites are associated with isolated Co. Spectroscopic data implied that the active species was Co 2+ in a tetrahedral environment, strongly bound to the silica. Others have also shown that isolated Co can exhibit selective C-H activation of alkanes [15][16][17]. For example, Hu et al used electrostatic adsorption of monomeric hexamminecobalt (III) with low metal loadings to produce silica-supported catalysts with isolated Co [15].…”