Ramli Anita, Khairul Anuar Nur Akila Syakida Idayu, Bakhtiar Nur Aielia Amira, Mohamad Yunus Normawati, Mohamed Alina Rahayu
HICoE Centre for Biofuel and Biochemical Research, Institute of Self-Sustainable Building, Universiti Teknologi PETRONAS, Seri Iskandar 32610, Perak, Malaysia.
Fundamental and Applied Sciences Department, Universiti Teknologi PETRONAS, Seri Iskandar 32610, Perak, Malaysia.
Molecules. 2023 Jun 24;28(13):4963. doi: 10.3390/molecules28134963.
Biomass lignin can be used to produce vanillin through an oxidation process. Although its purity is high, the processing time and separation efficiency are not ideal. This research aims to produce vanillin directly from Kenaf stalks without separating the lignin first from the lignocellulosic biomass. This method is greener because it does not require the separation of cellulose and hemicellulose from the biomass, thus minimizing the use of acid and alkaline solutions and saving time. A high oxygen storage capacity and release capacity of ceria as an oxidation catalyst contribute to the reversable redox properties between Ce and Ce in ceria lattice. Cerium oxide nanostructures were synthesized using a hydrothermal method treated under alkaline NaOH, followed by drying at 120 °C for 16 h and calcining at different temperatures between 400 and 600 °C for the direct oxidation of Kenaf stalks to vanillin under microwave irradiation. The catalysts were characterized for their physicochemical properties using XRD, N adsorption-desorption isotherms and TEM. All synthesized CeO nanostructures showed the presence of diffraction peaks assigned to the presence of cubic fluorite. The N adsorption-desorption isotherms showed that all catalysts possess a Type IV isotherm, indicating a mesoporous structure. The TEM image shows the uniform shape of the CeO nanostructures, while HRTEM images show that the CeO nanostructures are single-crystalline in nature. All catalysts were tested for the direct oxidation of Kenaf stalks using HO as the oxidizing agent in temperatures ranging from 160 to 180 °C for 10-30 min with 0.1-0.3 g catalyst loading under 100-500 W of microwave irradiation. The CeO-Nps-400 catalyst produced the highest vanillin yields of 3.84% and 4.32% for the direct oxidation of Kenaf stalks and extraction of lignin from Kenaf stalks, respectively. Compared to our earlier study, the highest vanillin yields of 2.90% and 3.70% for direct biomass and extracted lignin were achieved using a Ce/MgO catalyst.
生物质木质素可通过氧化过程用于生产香草醛。尽管其纯度较高，但处理时间和分离效率并不理想。本研究旨在直接从红麻秸秆中生产香草醛，而无需先从木质纤维素生物质中分离木质素。这种方法更环保，因为它不需要从生物质中分离纤维素和半纤维素，从而减少了酸碱溶液的使用并节省了时间。氧化铈作为氧化催化剂具有高储氧能力和释放能力，这有助于氧化铈晶格中Ce和Ce之间的可逆氧化还原性质。采用水热法在碱性NaOH条件下合成氧化铈纳米结构，然后在120℃干燥16 h，并在400至600℃之间的不同温度下煅烧，用于在微波辐射下将红麻秸秆直接氧化为香草醛。使用XRD、N吸附-脱附等温线和TEM对催化剂的物理化学性质进行了表征。所有合成的CeO纳米结构均显示出归属于立方萤石存在的衍射峰。N吸附-脱附等温线表明所有催化剂均具有IV型等温线，表明具有介孔结构。TEM图像显示了CeO纳米结构的均匀形状，而HRTEM图像表明CeO纳米结构本质上是单晶的。所有催化剂均以HO作为氧化剂用于红麻秸秆的直接氧化测试，在100-500 W微波辐射下，温度范围为160至180℃，反应10-30分钟，催化剂负载量为0.1-0.3 g。对于红麻秸秆的直接氧化和从红麻秸秆中提取木质素，CeO-Nps-400催化剂分别产生了最高的香草醛产率，分别为3.84%和4.32%。与我们早期的研究相比，使用Ce/MgO催化剂时，直接生物质和提取木质素的最高香草醛产率分别为2.90%和3.70%。
