Current Catalysis - Volume 8, Issue 1, 2019

Background: Core-magnetic composites offer unique possibilities to accommodate adequate amounts of acid-base and redox functional sites and hence to catalyze the biomass conversion reactions in a one-pot way. Moreover, due to the dual functionality, the core-magnetic composites provide a bridge between homogeneous and heterogeneous catalysis. Hence, this minireview aims to offer a comprehensive account of remarkable recent applications of core-magnetic composites in the catalytic processes for biomass valorization. Methods: A critical evaluation of synthetic methodologies utilized for the production of the magnetic nanoparticles, characterization techniques and catalytic applications is provided. Results: The benefits of their utilization are exemplified by most representative examples of one-pot transformation of cellulose and upgrading processes. Other recent examples constitute the lignin fragmentation on magnetic iron oxide-based catalysts and the renewable crude glycerol up-grading using core-shell magnetic iron oxide bio-based materials. Conclusion: The review provides important information on the distinctive properties of the functionalized core-magnetic composites. Moreover, this review offers useful information affording a largescale production development, in terms of catalyst and reaction conditions, tailoring selectivity, and the potential to regenerate the catalysts.

Valorization of lignocellulosic biomass becomes a sustainable alternative against the constant depletion and environmental problems of fossil sources necessary for the production of chemicals and fuels. In this context, a wide range of renewable raw materials can be obtained from lignocellulosic biomass in both polymeric (i.e. cellulose, starch, lignin) and monomeric (i.e. sugars, polyols, phenols) forms. Lignin and its derivatives are interesting platform chemicals for industry, although mainly due to its refractory characteristics its use has been less considered compared to other biomass fractions. To take advantage of the potentialities of lignin, it is necessary to isolate it from the cellulose/ hemicellulosic fraction, and then apply depolymerization processes; the overcoming of technical limitations being a current issue of growing interest for many research groups. In this review, significant data related to the structural characteristics of different types of commercial lignins are presented, also including extraction and isolation processes from biomass, and industrial feedstocks obtained as residues from paper industry under different treatments. The review mainly focuses on the different depolymerization processes (hydrolysis, hydrogenolysis, hydrodeoxygenation, pyrolysis) up to now developed and investigated analyzing the different hydrocarbons and aromatic derivatives obtained in each case, as well as the interesting reactions some of them may undergo. Special emphasis is done on the development of new catalysts and catalytic processes for the efficient production of fuels and chemicals from lignin. The possibilities of applications for lignin and its derivatives in new industrial processes and their integration into the biorefinery of the future are also assessed.

Background: To prevent the environmental pollution, the release of the carcinogenic reagents like nitroarenes, especially nitrobenzene must be reduced or to find a way to convert these hazardous materials into less harmful material. For the reduction of nitroarenes, various types of catalysts such as metal nanoparticles (mainly coinage and group VIII) and platinum group metals were used. The chemo/homo selectivity of the reduction of nitroarenes was tested mainly in an organic solvent medium. Method: Trimetallic oxide nanocatalysts were prepared chemically and characterized via Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM) and solid UV studies. A series of nitroarenes were subjected to get their amine analogues using the NaBH4 in an aqueous medium using the synthesized catalysts. The completion of the reduction process was confirmed by the spectroscopic analysis. Results: The average crystallite of the trimetallic oxide nanocatalysts was found to be 14-32nm. The reductions were selective (homo/chemo) and kinetics followed the Lindemann-Hinshelwood pseudofirst order kinetics with the rate constant in the order of 10-3 s-1. Hydroxylamine intermediate was found to be formed in the reduction procedure. Conclusion: The catalysts showed promising for the selectivity (homo/chemo). The reduction processes were less time consuming e.g. nitrobenzene took 10 mins and a series of nitroanilines required 35-40 s for the reduction. In short, the trimetallic nano-oxide catalysts possess fast reaction process, cost-effective, easy to handle, reusable and hence could be promising for industrial waste treatment.

In this article, we explored the possibility of controlling the reactivity of ZnO nanostructures by modifying its surface with gold nanoparticles (Au NPs). By varying the concentration of Au with different wt% (x = 0.01, 0.05, 0.08, 1 and 2), we have synthesized a series of (ZnO/Aux) nanocomposites (NCs). A thorough investigation of the photocatalytic performance of different wt% of Au NPs on ZnO nanosurface has been carried out. It was observed that ZnO/Au0.08 nanocomposite showed the highest photocatalytic activity among all concentrations of Au on the ZnO surface, which degrades the dye concentration within 2 minutes of visible light exposure. It was further revealed that with an increase in the size of plasmonic nanoparticles beyond 0.08%, the accessible surface area of the Au nanoparticle decreases. The photon absorption capacity of Au nanoparticle decreases beyond 0.08% resulting in a decrease in electron transfer rate from Au to ZnO and a decrease of photocatalytic activity. Background: Due to the industrialization process, most of the toxic materials go into the water bodies, affecting the water and our ecological system. The conventional techniques to remove dyes are expensive and inefficient. Recently, heterogeneous semiconductor materials like TiO2 and ZnO have been regarded as potential candidates for the removal of dye from the water system. Objective: To investigate the photocatalytic performance of different wt% of Au NPs on ZnO nanosurface and the effect of the size of Au NPs for photocatalytic performance in the degradation process. Method: A facile microwave method has been adopted for the synthesis of ZnO nanostructure followed by a reduction of gold salt in the presence of ZnO nanostructure to form the composite. Results: ZnO/Au0.08 nanocomposite showed the highest photocatalytic activity which degrades the dye concentration within 2 minutes of visible light exposure. The schematic mechanism of electron transfer rate was discussed. Conclusion: Raspberry shaped ZnO nanoparticles modified with different percentages of Au NPs showed good photocatalytic behavior in the degradation of dye molecules. The synergetic effect of unique morphology of ZnO and well anchored Au nanostructures plays a crucial role.

Background: Layered double hydroxides (LDH) are drawing much attention as solid catalysts in recent years and have applications in various organic transformations as they possess a variety of basic sites which could be obtained by exchange of metal ions or by intercalation of suitable anions into their interlayer space. Ru based complexes have widespread catalytic applications in many organic reactions. Herein, novel ruthenium containing ternary LDH has been synthesized and used as a multifunctional catalyst for Aldol condensation and transfer hydrogenation reactions. Methods: Ternary LDH multifunctional catalyst containing Mg, Ru and Al was prepared by coprecipitation and hydrothermal treatment. The catalyst was characterized by elemental analysis, Powder XRD, FT-IR, BET, TGA, DRS, SEM, EDX, XPS and TEM. The products of the reactions were characterized by 1H NMR and GC-MS. Results: The analysis of catalyst revealed incorporation of Ru in the brucite layers of the LDH and showed the mosaic single crystal with BET surface area of 84.25 m2 g-1. This catalyst yielded 85–98% products for Aldol condensation reactions within 4 h reaction time, and 82–98% products for transfer hydrogenation reactions within 16 h reaction time. Conclusion: The resultant MgRuAl-LDH with acid and base sites was found to be highly active and selective for one-step synthesis of nitrile compounds. The catalyst works more efficiently for Aldol condensation reactions in shorter reaction times compared to transfer hydrogenation reactions.