Popova Margarita, Boycheva Silviya, Dimitrov Ivan, Dimitrov Momtchil, Kovacheva Daniela, Karashanova Daniela, Velinov Nikolay, Atanasova Genoveva, Szegedi Agnes
Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria.
Department of Thermal and Nuclear Power Engineering, Technical University of Sofia, 8 Kl. Ohridsky Blvd., 1000 Sofia, Bulgaria.
Molecules. 2024 Dec 5;29(23):5753. doi: 10.3390/molecules29235753.
Zeolites with different structures (P1, sodalite, and X) were synthesized from coal fly ash by applying ultrasonically assisted hydrothermal and fusion-hydrothermal synthesis. Bimetallic catalysts, containing 5 wt.% Ni and 2.5 wt.% Cu, supported on the zeolites, were prepared by a post-synthesis incipient wetness impregnation method. The catalysts were characterized by X-ray powder diffraction (XRPD), N physisorption, transmission electron microscopy (TEM), Mössbauer and X-ray photoelectron spectroscopies (XPS), and H-temperature-programmed reduction (H-TPR) analyses. The XRPD results showed that crystalline Cu and NiCu intermetallic nanoparticles were formed in the reduced catalysts. The presence of the intermetallic phase affected the reducibility of the nickel by shifting it to a lower temperature, as confirmed by the H-TPR curves. Based on the Mössbauer spectroscopic results, it was established that the iron contamination of the coal fly ash zeolites (CFAZs) was distributed in ionic positions of the zeolite lattice and as a finely dispersed iron oxide phase on the external surface of the supports. The formation of the NiFe alloy, not detectable by XRPD, was also evidenced on the impregnated samples. The catalysts were studied in the upgrading of levulinic acid (LA), derived from lignocellulosic biomass, to γ-valerolactone (GVL), in a batch reactor under 30 bar H pressure at 150 and 200 °C, applying water as a solvent. The NiCu/SOD and NiCu/X catalysts showed total LA conversion and a high GVL yield (>75%) at a reaction temperature of 200 °C. It was found that the textural parameters of the catalysts have less influence on the catalytic activity, but rather the stable dispersion of metals during the reaction. The characterization of the spent catalyst found the rearrangement of the support structure. The high LA conversion and GVL yield can be attributed to the weak acidic character of the support and the moderate hydrogenation activity of the Ni-Cu sites with high dispersion.
通过超声辅助水热法和熔融水热法，由粉煤灰合成了具有不同结构（P1、方钠石和X型）的沸石。采用合成后初湿浸渍法制备了负载在沸石上的含5 wt.%镍和2.5 wt.%铜的双金属催化剂。通过X射线粉末衍射（XRPD）、N物理吸附、透射电子显微镜（TEM）、穆斯堡尔谱和X射线光电子能谱（XPS）以及H程序升温还原（H-TPR）分析对催化剂进行了表征。XRPD结果表明，在还原后的催化剂中形成了结晶态的铜和镍铜金属间纳米颗粒。金属间相的存在通过将镍的还原温度降低，影响了镍的还原性能，H-TPR曲线证实了这一点。基于穆斯堡尔光谱结果，确定粉煤灰沸石（CFAZs）中的铁杂质分布在沸石晶格的离子位置以及载体外表面的细分散氧化铁相中。在浸渍样品上也证实了XRPD无法检测到的NiFe合金的形成。在间歇式反应器中，以水为溶剂，在30 bar氢气压力、150和200 °C条件下，研究了这些催化剂对木质纤维素生物质衍生的乙酰丙酸（LA）升级为γ-戊内酯（GVL）的性能。在200 °C的反应温度下，NiCu/SOD和NiCu/X催化剂表现出乙酰丙酸的完全转化和较高的γ-戊内酯产率（>75%）。研究发现，催化剂的结构参数对催化活性影响较小，而反应过程中金属的稳定分散更为重要。对失活催化剂的表征发现载体结构发生了重排。较高的乙酰丙酸转化率和γ-戊内酯产率可归因于载体的弱酸性以及高分散的Ni-Cu位点的适度加氢活性。
