Abstract <p>The transformation of agricultural waste into an effective catalyst will not only provide energy but also help to minimize waste disposal issues. In this study, leftover eggshell powder was calcined at 900 °C to obtain CaO powder, which was subsequently incorporated with Ag and Cu nanoparticles synthesized via a green route using Polyalthia longifolia plant extract. Four catalysts categorized as CaO, Ag/CaO, Cu/CaO, and Ag–Cu/CaO were prepared and utilized separately in the transesterification reaction. Rice bran oil was used to produce FAMEs using the four catalysts separately. XRD analysis confirmed the crystallinity of CaO as well as the impregnation of Ag and Cu nanoparticles on the surface of CaO. A slight change in surface chemistry due to the incorporation of metal nanoparticles was verified by FTIR spectra, whereas TGA analysis showed minimum weight loss for metal-incorporated CaO, which may be attributed to the change in surface behavior of CaO by the impregnation of metal nanoparticles. SEM analysis revealed the surface roughness and distribution of metal nanoparticles on CaO. BET results showed a low surface area of Ag–Cu/CaO. The Ag–Cu/CaO catalyst, even with a low surface area, provided a maximum biodiesel yield of 98.9 ± 0.2% at optimum reaction conditions (oil to methanol 1:9, reaction time 3 h, temperature 65 °C, catalyst loading 3 wt.%). This high yield may arise from increased surface basicity, improved dispersion of metal nanoparticles, or possible synergistic interaction between Ag and Cu. The single-metal-impregnated catalyst, such as Ag/CaO, provided 92.4 ± 0.3% biodiesel yield, while Cu/CaO provided 93.3 ± 0.3% yield under optimum conditions. The neat CaO catalyst yielded only 88% at optimum conditions. The Changes in the surface of CaO resulting from impregnation with metal nanoparticles and the possible synergistic effect between the metals and CaO may account for the increase in biodiesel yield from CaO, Ag/CaO, Cu/CaO and Ag–Cu/CaO. The biodiesel prepared using the Ag–Cu/CaO catalyst under optimal conditions was analyzed by GC–MS to confirm the preparation of unsaturated fatty acid methyl esters (FAMEs). In addition, biodiesel characteristics, such as cloud point, pour point, flash point, and density, were investigated and compared with ASTM D6751 standards. The findings revealed that waste-derived CaO impregnated with green-synthesized Ag and Cu nanoparticles can be utilized in heterogeneous catalysis for efficient biodiesel production.</p> Graphical Abstract <p></p>

Synergistic Bimetallic Catalysts on Green CaO Support for Enhanced Biodiesel Yield

期刊论文
发表日期：

2026年3月20日

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Ali Murad,
Parveen Akhter,
Murid Hussain

摘要

Abstract

The transformation of agricultural waste into an effective catalyst will not only provide energy but also help to minimize waste disposal issues. In this study, leftover eggshell powder was calcined at 900 °C to obtain CaO powder, which was subsequently incorporated with Ag and Cu nanoparticles synthesized via a green route using Polyalthia longifolia plant extract. Four catalysts categorized as CaO, Ag/CaO, Cu/CaO, and Ag–Cu/CaO were prepared and utilized separately in the transesterification reaction. Rice bran oil was used to produce FAMEs using the four catalysts separately. XRD analysis confirmed the crystallinity of CaO as well as the impregnation of Ag and Cu nanoparticles on the surface of CaO. A slight change in surface chemistry due to the incorporation of metal nanoparticles was verified by FTIR spectra, whereas TGA analysis showed minimum weight loss for metal-incorporated CaO, which may be attributed to the change in surface behavior of CaO by the impregnation of metal nanoparticles. SEM analysis revealed the surface roughness and distribution of metal nanoparticles on CaO. BET results showed a low surface area of Ag–Cu/CaO. The Ag–Cu/CaO catalyst, even with a low surface area, provided a maximum biodiesel yield of 98.9 ± 0.2% at optimum reaction conditions (oil to methanol 1:9, reaction time 3 h, temperature 65 °C, catalyst loading 3 wt.%). This high yield may arise from increased surface basicity, improved dispersion of metal nanoparticles, or possible synergistic interaction between Ag and Cu. The single-metal-impregnated catalyst, such as Ag/CaO, provided 92.4 ± 0.3% biodiesel yield, while Cu/CaO provided 93.3 ± 0.3% yield under optimum conditions. The neat CaO catalyst yielded only 88% at optimum conditions. The Changes in the surface of CaO resulting from impregnation with metal nanoparticles and the possible synergistic effect between the metals and CaO may account for the increase in biodiesel yield from CaO, Ag/CaO, Cu/CaO and Ag–Cu/CaO. The biodiesel prepared using the Ag–Cu/CaO catalyst under optimal conditions was analyzed by GC–MS to confirm the preparation of unsaturated fatty acid methyl esters (FAMEs). In addition, biodiesel characteristics, such as cloud point, pour point, flash point, and density, were investigated and compared with ASTM D6751 standards. The findings revealed that waste-derived CaO impregnated with green-synthesized Ag and Cu nanoparticles can be utilized in heterogeneous catalysis for efficient biodiesel production.

Graphical Abstract