Insights into the Influence of ZrO₂ Crystal Structures on Methyl Laurate Hydrogenation over Co/ZrO₂ Catalysts

Abstract

Six kinds of ZrO2 supports (ZRX, X = 1–6) with different crystal structures (monoclinic ZrO2: m-ZrO2; tetragonal ZrO2: t-ZrO2; and mixed-phase of monoclinic and tetragonal ZrO2: mix-ZrO2) were synthesized, and their effects on the properties of Co/ZrO2 catalysts were investigated for methyl laurate hydrogenation. Among the prepared catalysts, Co/mix-ZrO2 (Co/ZR3), with the highest concentration of surface Co2+, oxygen vacancies (Ov), and complex types of exposed Co crystal planes, exhibited the highest activity and stability toward methyl laurate hydrogenation, with nearly 100% yield of liquid alkanes produced at 240 °C, or 90.5% of fatty alcohol (selectivity: 96%) at 180 °C. By exploring reaction kinetics and catalyst properties, oxygen vacancies in the support of Co/ZrO2 catalysts were found to play an important role in tuning the valence state of Co, while the crystal structure of ZrO2 influenced exposed lattice planes of cobalt. The high Ov content and active β-Co(102) crystal face of Co/ZR3 were efficient for reducing activation energies for C–C or CO bond cleavage, causing high activity toward fatty ester hydrogenation. Less-active Co, such as α-Co(111) and α-Co(200), or oxygen vacancies made the fatty alcohol intermediate difficult to be deoxygenated to alkanes.

Chromium Oxide‐modified Mesoporous Zirconium Dioxide: Efficient Heterogeneous Catalyst for the Synthesis of 5‐Hydroxymethylfurfural

“…Generally, active sites of the catalysts can be divided into three regions, weak (50-200 °C), medium (200-350 °C), and strong (350-650 °C) NH 3 adsorption sites. [37] As shown in Figure 3, the surface acidity of Cr/ZrO 2 catalysts varied significantly as the ratio of Cr loading increasing. The weak (peaks near 110 °C) and medium acid sites (peaks near 270 and 350 °C) of all catalysts could be derived from surface acidic -OH groups (e. g., ZrÀ OH and CrÀ OH) and the strong acid sites (350-650 °C) may be attributed to the coordinated unsaturated Zr δ + ions.…”

“…The presence of Cr 6 + may be due to the low content of the Cr element and the metal-support interaction of Cr 3 + with oxygen on the surface of ZrO 2 or the oxidization of Cr 3 + being exposed in the air. [37] Besides, 15 % Cr/ZrO 2 catalyst owned the higher the content of Cr on the catalyst's surface, indicating its better catalytic performance. The O 1s XPS spectra of the catalysts were shown in Figure 4c.…”

“…The XPS results also confirmed the coexistence of two different Cr species (Cr 3+ of Cr 2 O 3 and Cr 6+ ) on the surfaces of the catalyst (Figure 4b). The presence of Cr 6+ may be due to the low content of the Cr element and the metal‐support interaction of Cr 3+ with oxygen on the surface of ZrO 2 or the oxidization of Cr 3+ being exposed in the air [37] . Besides, 15 % Cr/ZrO 2 catalyst owned the higher the content of Cr on the catalyst's surface, indicating its better catalytic performance.…”

Bimetallic single atom promoted α-MnO2 for enhanced catalytic oxidation of 5-hydroxymethylfurfural

“…Therefore, many previous research studies have directly correlated O ads with the concentration of surface defects, particularly O v-S . 37–39 In Fig. 5, Pd/MnO 2 has a slightly higher ratio of O ads (16.0%) than un-doped MnO 2 (13%).…”

“…S14†). 20,37 O ads usually contains several reactive species such as O 2− , O 2 2− , and O − that are decorated at surface defects. Therefore, many previous research studies have directly correlated O ads with the concentration of surface defects, particularly O v-S .…”