Propane Dehydrogenation to Propylene and Propylene Adsorption on Ni and Ni‐Sn Catalysts

Abstract

Temperature programmed reaction (TPR) measurements with propane over silica-supported Ni, NiÀ Sn and Sn catalysts show that the reaction products change significantly from mostly methane, hydrogen and surface carbon over Ni to propylene and hydrogen over NiÀ Sn. Propylene formation over NiÀ Sn starts at a moderate temperature of 630 K. Since the activity of Sn by itself is low, Sn serves as a promoter for Ni. The promoter effects are attributed to a lower adsorption energy of molecularly adsorbed propylene and suppression of propylidyne formation on NiÀ Sn based on temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS) measurements as well as density functional theory (DFT) calculations for propylene adsorption on Ni(110) and c(2 × 2)-Sn/Ni(110) single-crystal surfaces. On Ni, propylene forms a π-bonded structure with ν(C=C) at 1500 cm À 1 , which desorbs at 170 K, and a di-σ-bonded structure with ν(C=C) at 1416 cm À 1 , which desorbs at 245 K. The di-σ-bonded structure is asymmetric, with the methylene C atom being in the middle of the NiÀ Ni bridge site, and the methylidyne C atom being above one of these Ni atoms. Therefore, this structure can also be characterized as a hybrid between di-σ-and π-bonded structures. Only a fraction of propylene desorbs from Ni because propylene can convert into propylidyne, which decomposes further. In contrast, propylene forms only a π-bonded structure on NiÀ Sn with ν(C=C) at 1506 cm À 1 , which desorbs at 125 K. The low stability of this structure enables propylene to desorb fully, resulting in high reaction selectivity in propane dehydrogenation to propylene over the NiÀ Sn catalyst.

Spectroscopic observation and structure-insensitivity of hydroxyls on gold

“…Similar cluster and periodic structure models were previously successfully used to describe oxygen, H 2 O 2 and OOH adsorption on Au and other adsorbates on multiple surfaces. 9,13,15,18–28 The calculations show that on most Au surfaces hydroxyls preferentially adsorb on a bridge Au–Au site, with ν (O–H) being in a narrow range from 3683 to 3687 cm −1 (Fig. 2).…”

“…Our previous catalytic studies with supported Au and other metals successfully used the same preparation method. [9][10][11][12][13][14][15] The Au loading was varied between 0.25 and 2 wt%. Details of the experimental and computational methods are provided in the ESI.…”

Kinetics and Reaction Mechanisms of Acetic Acid Hydrodeoxygenation over Pt and Pt–Mo Catalysts

“…After Mo deposition, the Pt–Mo catalyst was dried and calcined with the same procedure. Similar catalyst synthesis methods were used previously for studying other supported metal catalysts. ,− …”

“…The positions of the Pt atoms in the bottom two layers were constrained, simulating the bulk structure of Pt nanoparticles. Similar computational settings were previously used for studying adsorption and reactivity on multiple metallic catalytic surfaces. ,,− …”

Insights into the Nature of Selective Nickel Sites on Ni/Al2O3 Catalysts for Propane Dehydrogenation

“…Alternatively, Ni-based catalysts have garnered interest because of its appealing ability to activate alkane molecules. Nevertheless, supported metallic Ni NP catalysts exhibit a high intrinsic activity toward C–C breaking, leading to the formation of methane, hydrogen, and coke. , Previous strategies for minimizing the C–C cleavage, such as adding P and S promoters to dilute the large nickel ensembles have been shown to work but suffer from the loss of promoters at high temperatures during the regeneration process. − By means of anchoring Ni precursors on defect-containing supports, such as heteroatom-doped sp 2 carbon materials, metal organic frameworks (MOFs), and two-dimensional layered MoS 2 , supported nickel single-site catalysts for electro-catalysis and other reactions under mild conditions have been reported. − To date, it remains a challenge to prepare supported nickel catalysts in an exclusively single-site configuration and prevent the reduction of Ni­(II) and formation of Ni NPs under the rigorous reaction and regeneration conditions of PDH.…”