Abstract
The design and new synthetic protocols for ABO3 perovskite catalysts holds a promise that these catalysts can be used in practical applications. In this study, we prepared using the sol-gel method. Specifically, noble metal-containing La-based perovskites (LaInO3, LaIrO3, and LaPtO3) were synthesized for Section A of the synthesis chapter. In Section B, we explored the effects of A-site and B-site replacement by synthesizing LaCoO3, LaNiO3, and CeCoO3. A suite of analytical techniques was used to confirm the formation of ABO3 perovskite catalysts. Brunauer-Emmett- Teller (BET) surface areas of the catalysts: LaPtO3, LaInO3, and LaIrO3 using nitrogen at 77K gave 0.993 m2/g, 3.338 m2/g, and 4.112 m2/g, respectively. Tolerance factors ranged from 0.79 to 0.86, confirming their theoretical stability, and thermogravimetric (TGA) analysis showed that the LaInO3 should not be used for reactions above 100 ℃ due to lack of thermal stability compared to other as-synthesized perovskites. In Section B, LaNiO3 had the lowest surface area (6.644 m2/g), followed by LaCoO3 (9.458 m2/g) and CeCoO3 (20.528 m2/g), with tolerance factors between 0.801 and 0.832 signifying their theoretical stability. With the XRD and SEM confirming the presence of the metals and the formation of the perovskites.
We evaluated the catalytic performance of LaInO3 and LaPtO3 perovskites with ethanol as a hydrogen donor for the hydrogenation of levulinic acid (LA). The reaction yielded ethyl levulinate (EL) via esterification and α-angelica lactone (AL) via hydrogenation, with LaInO3 showing superior reactivity compared to LaPtO3. These products formation was confirmed by NMR and GC-MS. Detailed analysis under varying conditions revealed a high conversion rate of 78% at 9 hours. Recyclability tests indicated deactivation of LaInO3 over consecutive cycles.
We further assessed the influence of La and Ce at the A-site, and Ni and Co at the B-site of the perovskite structure, to identify optimal catalysts for LA transformation without noble metals. Our results indicated that Ce outperformed La as an A-site candidate. CeCoO3 emerged as the most effective catalyst, achieving complete conversion at 90°C with a 100% yield of EL. Hydrogenation of LA using molecular hydrogen (H2) exhibited superior catalytic conversion compared to CTH reactions. LaPtO3 achieved a maximum conversion of 94% at 30 bars of H2, with a minimum of
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82% at 10 bars. LaInO3 showed the highest conversion of 97% at 30 bars and a minimum of 75% at 10 bars, demonstrating that increased pressure activates the catalyst’s active sites, enhancing conversion rates.
In overall, we have successfully synthesized the ABO3 perovskite catalyst. The synthesized catalysts were examined using various characterization techniques. Catalytic studies revealed that LaInO3 and CeCoO3 catalysts were the best catalysts for transfer catalytic hydrogenation (CTH). While for direct hydrogenation LaInO3 and LaPtO3 showed superior conversions.