A Study on the Oxygen Vacancies in ZnPd/ZnO‐Al and their Promoting Role in Glycerol Hydrogenolysis

Abstract

The relationship between catalyst structure and catalytic activity is an important and challenging topic for researchers in the field of catalysis. In this work, the effect of oxygen vacancies on the activity of ZnPd/ZnO‐Al catalysts was studied in an important reaction—glycerol hydrogenolysis. Interestingly, the catalytic activity improved significantly with the addition of a small amount of Al, and high selectivity to 1,2‐propanediol (>90 %) was achieved in glycerol hydrogenolysis over ZnPd/ZnO‐Al catalysts. Importantly, the formation of oxygen vacancies benefits from the substitution of Al atoms, and the Al content in the ZnO lattice is related to the oxygen vacancies density and catalytic activity. Moreover, the important role played by oxygen vacancies in glycerol hydrogenolysis has been discussed in detail.

Selective Hydrogenolysis of Glycerol to Propylene Glycol on Supported Pd Catalysts: Promoting Effects of ZnO and Mechanistic Assessment of Active PdZn Alloy Surfaces

“…29 The PdZn catalysts were mainly prepared via the reduction of dispersed Pd precursors on ZnO-based supports. However, the use of ZnO encounters two problems: (a) the Zn/Pd ratio of the PdZn alloys cannot be mediated, which is critical for the catalytic activity of the PdZn alloys, 34,35 and (b) the ZnO support is unstable in glycerol hydrogenolysis reactions because of its poor hydrothermal stability 28 thus needs to be stabilized by structural promoters (e.g., Al 2 O 3 ). 29 Glycerol hydrogenolysis to propylene glycol on metal surfaces in neutral and basic aqueous solutions involves glycerol dehydrogenation to glyceraldehyde, glyceraldehyde dehydration to 2-hydroxyacrylaldehyde, and sequential hydrogenations of 2-hydroxyacrylaldehyde to acetol and propylene glycol (Scheme 1).…”

“…Introduction of additional metals (e.g., Co, , Fe, , and Zn , ) to monometallic Pd catalysts can modify the properties of the Pd surface and consequently improve its glycerol hydrogenolysis rate and selectivity to propylene glycol. In particular, significant attention has been paid to bimetallic Pd–Zn catalysts because of the readily formation of uniform PdZn alloys and their wide applications, not only in glycerol hydrogenolysis , but also in other reactions, such as methanol reforming − and water–gas shift reactions. , In particular, a high propylene glycol selectivity of 92.3% was obtained at 80.4% glycerol conversion for glycerol hydrogenolysis on a PdZn/ZnO@Al 2 O 3 catalyst at 503 K and 3 MPa H 2 . The PdZn catalysts were mainly prepared via the reduction of dispersed Pd precursors on ZnO-based supports.…”

“…The PdZn catalysts were mainly prepared via the reduction of dispersed Pd precursors on ZnO-based supports. However, the use of ZnO encounters two problems: (a) the Zn/Pd ratio of the PdZn alloys cannot be mediated, which is critical for the catalytic activity of the PdZn alloys, , and (b) the ZnO support is unstable in glycerol hydrogenolysis reactions because of its poor hydrothermal stability and thus needs to be stabilized by structural promoters (e.g., Al 2 O 3 ) …”

Bimetallic Effects of Silver‐Modified Nickel Catalysts and their Synergy in Glycerol Hydrogenolysis

“…[2,3] This reaction is also very important as an appropriate model reaction to study the selectivec leavage of CÀO and CÀCb onds in the catalytic dehydroxylation of biomass-derived polyols, [4][5][6] which is regardeda sa ni mportant process for future biorefineries. [7,8] To better understand the reaction mechanism of hydrogenolysis as ag uideline to select suitable metal catalysts and cocatalysts to improve the product selectivity,i ntensive studies on various metal catalysts, which mainly include Ru-, [9][10][11][12][13][14] Cu-, [12,[15][16][17][18][19] Pt-, [9,12,20,21] and Pd-based catalysts, [22,23] for glycerolh ydrogenolysis have been conducted. Ni is ap romisingc atalystf or hydrogenolysis because of its low cost, high activity,a nd resistance to poisoning [24,25] but it shows poor hydrothermal stability compared to noble-metal catalysts [26] and low hydrogenolytic activity toward CÀOb ond compared to Cu catalysts.…”

Catalytic hydrodeoxygenation of palmitic acid over a bifunctional Co-doped MoO2/CNTs catalyst: an insight into the promoting effect of cobalt

“…Generally, the introduction of a suitable dopant (called metal modification) would bring a pronounced enhancement in activity, selectivity, and stability due to the formation of defects, new active sites, and acidic or basic sites. [18][19][20][21][22] For instance, Co is selected as a dopant in the Ni-Mo-Co system to change the electronic properties of adjacent Mo atoms, resulting in an increase of catalytic activity and satisfactory stability in the HDO of phenol. 23 Accordingly, in our present work, Co is intentionally selected as the dopant to achieve the metal modification of MoO 2 /CNTs catalyst to further improve the catalytic performance.…”