Kinetic Control of Hexagonal Mg(OH)₂ Nanoflakes for Catalytic Application of Preferential CO Oxidation

Abstract

Controlling the growth of nanocrystals is one of the most challenged issues in current catalytic field, which helps to further understand the size and morphology related behaviors for catalytic applications. In this work, we investigated the plane growth kinetics of Mg(OH) 2 for catalytic application in preferential CO oxidation. Nanoflakes were synthesized through hydrothermal method. The morphology and structure of nanoflakes were characterized by TEM, SEM, and XRD. By varying the reaction temperature and time, Mg(OH) 2 nanoflakes underwent an anisotropic growth. Benefited from the Ostwald ripening process, the thickness of nanoflake corresponding to the (110) plane of Mg(OH) 2 was tuned from 7.6 nm to 24.0 nm, while the diameter of (001) plane increased from 18.2 nm to 30.2 nm. The grain growth kinetics for the thickness was well described in terms of an equation, D 5 ＝7.6 5 ＋6.9×10 8 exp(28.14/RT). After depositing Pt nanoparticles onto these Mg(OH) 2 nanoflakes, an excellent catalytic performance was achieved for preferential CO oxidation in H 2 -rich streams with a wide temperature window from 140 ℃ to 240 ℃ for complete CO conversion due to the interaction between Pt and hydroxyl groups. The findings reported here would be helpful in discovering novel catalysts for application of proton exchange membrane fuel cells.

Kinetic control of CeO2 nanoparticles for catalytic CO oxidation

“…Using MATLAB software (Mathworks, Natick, MA), the growth process of CeO 2 nanoparticles was in good agreement with the OR process. The similar OR process has been reported in other systems, such as SnO 2 [20], Mg(OH) 2 [21], NiFe 2 O 4 [22], and YVO 4 [23].…”

Zinc Ferrite Nanoparticles: Unusual Growth Mechanism for Size‐Dependent Properties

“…The grain growth of Zn 0.86 Fe 2.14 O 4+δ NPs also changes their lattice parameters, as observed for many other oxide nanocrystals [21,22] . X‐ray diffraction patterns of Zn 0.86 Fe 2.14 O 4+δ NPs were refined by GSAS software (Figure S10).…”

“…), simple metal oxide (SnO 2 , [18,19] TiO 2 , [20] etc. ), metal hydroxide (Mg(OH) 2 ), [21] and partial polymetallic oxides (NiFe 2 O 4 [22] ), etc.. However, it has not delivered a coherent explanation about the evolution of magnetic non‐stoichiometric zinc ferrite with spinel structure, especially in the hydrothermal reaction that have been widely used to synthesize nanocrystals.…”

Understanding the Doping Chemistry of High Oxidation States in Scheelite CaWO4 by Hydrothermal Conditions

“…Similar observations have been reported for many other oxide nanocrystals. 38,39 From the HRTEM images of the selected nanocrystals (insets of Figure S4), one can see that the interplanar spacing between adjacent lattice fringes was 0.312, 0.311, 0.311, 0.311, and 0.312 nm for SS-10, K-200-10, K-160-10, NH 4 -200-10, and NH 4 -160-10 samples, respectively, which are close to the values of 0.312, 0.311, 0.311, 0.311, and 0.311 nm for the (112) plane calculated by Rietveld refinements, respectively, but slightly larger than that (0.310 nm) observed for CaWO 4 (JCPDS card no. .…”