The_Catalyst_Review_January_2024 - 17

Nickel-Tin Nanoalloy Supported ZnO Catalysts from Mixed-metal Zeolitic Imidazolate Frameworks
for Selective Conversion of Glycerol to 1,2-Propanediol
Biomass conversion processes have made large quantities of glycerol available for industrial use to produce value-added chemicals such as
1,2-propanediol (1,2-PDO). Although 1,2-PDO is typically produced from propylene oxide, catalytic hydrogenolysis of glycerol represents
a potentially more cost-effective, environmentally friendly route. Herein, the authors describe the synthesis of mixed metal (MM) zeolitic
imidazolate frameworks (ZIFs) as a precursor to Ni-Sn-based catalysts exhibiting excellent catalytic performance and selectivity for glycerol
hydrogenolysis.
These workers began by incorporating Ni and Sn ions into a Zn-based ZIF using an in-situ method followed by successive calcination
and reduction processes to produce well-dispersed Ni-Sn nanoalloys (~7 nm) supported ZnO catalysts, MM-ZIF_R500, (Scheme 1). The
composition of Ni/Sn can be systematically controlled so that the difference in the metal ion incorporation can be observed. Metal ion
incorporation profoundly affects the structural characteristics of the resulting Ni-Sn/ZnO catalysts, as well as the formation of various phases of
Ni-Sn and Ni-Zn alloys, the sizes of different particles, and acid strength.
Scheme 1. Schematic illustration of synthesis of ZIF-derived NixSny nanoalloy on ZnO catalysts.
Glycerol hydrogenolysis was then conducted using the prepared MM-ZIF catalysts in order to evaluate their performance. 3Ni1Sn/ZnO_R500
showed the best catalytic performance and produced the highest yield (94.2%) of 1,2-PDO at ~100% conversion of glycerol. It also showed
low apparent activation energy (15.4 kJ/ mol) and excellent stability. The results demonstrated that the synergy between Ni-Sn alloy, finely
dispersed Ni metallic sites, and the Lewis acidity of SnOx species-loaded ZnO play a pivotal role in the high activity and selectivity of the
catalyst.
The detection of acetol as an intermediate during these evaluations strongly suggests that the reaction route involves dehydration, followed by
hydrogenation (Scheme 2). Although the selective hydrogenolysis of glycerol can produce 1,2-PDO or 1,3-PDO' the selectivity for 1,3-PDO was
extremely low (~1%), indicating that the removal of the primary hydroxyl group is more probable than the removal of the secondary hydroxyl
group. Because the dehydration of hydroxyl groups is most prominent over the Lewis acid sites, it is likely that the dehydration of the primary
hydroxyl group proceeds due to the presence of high oxophilic SnOx and ZnO. Nimbalkar AS, Oh K-R, Han SJ, et al. (2023). ChemSusChem,
doi.org/10.1002/cssc.202301315
Scheme 2. Proposed reaction pathway for the production of 1,2-PDO from glycerol over xNiySn-ZIF_R500 catalyst.
The Catalyst Review
January 2024
17

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