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Excessive emission of CO2 into the atmosphere has severely impacted the global ecological environment. Converting CO2 into valuable chemicals and fuels is of great significance for sustainable development. However, low activity and undesirable selectivity often result from the inherent inertness of CO2. Herein, K- or/and Zn-modified Fe-based catalysts were prepared by an incipient-wetness impregnation method for CO2 hydrogenation via a cascade reaction. The results indicate that K species exist as K2O while Zn species exist as ZnFe2O4. In the CO2 hydrogenation pathway, K2O facilitates the adsorption of CO2 and restrains the adsorption of H2, accelerating the transformation of CO2 into C2–C4 olefins rather than paraffins while Zn species promote the dispersion of Fe species, leading to improved activity. Synergistically, a K- and Zn-modified Fe-based catalyst (2Zn–10K–Fe/Al) shows excellent catalytic CO2 hydrogenation activity, achieving a CO2 conversion of 77% which is 1.8 times that (42%) of the unmodified Fe-based catalyst (Fe/Al). Our catalyst also shows a significantly promoted selectivity to C2–C4 olefins of 17% in comparison with the Fe/Al catalyst (0%). It is envisioned that such a binary effect of elements might contribute to the low-cost and industrial production of Fe-based catalysts for selective CO2 conversion. [ABSTRACT FROM AUTHOR]

Hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) is a key reaction in the conversion of biomass to renewable fuels and value-added chemicals. Developing low-cost, highly efficient and reusable non-noble metal-based heterogeneous catalysts is vital but challenging. Herein, non-noble Ni–Mn/SiO2 catalysts with a low Ni loading (2.0 wt%) were designed for the selective hydrogenation of LA to GVL. The results showed that the optimal Ni–Mn/SiO2 (Ni/Mn = 2) catalyst with well-dispersed and small-sized metal nanoparticles (2.21 nm) and moderate acid sites exhibited excellent activity and selectivity and achieved a 100% yield of GVL in a 1,4-dioxane solvent under mild reaction conditions (e.g., 0.8 mol% Ni, 140 °C and 2.0 MPa H2) for 5.5 h and a 100% GVL yield at 180 °C for 2 h with a turnover frequency (TOF) of 190.2 h−1, which is better than most non-noble metal catalysts reported. Furthermore, the catalyst exhibited excellent reusability and could be recycled at least five times with only slight activity loss. This work provides new insights for the rational design of highly efficient and stable non-noble metal catalysts for the conversion of LA to GVL. [ABSTRACT FROM AUTHOR]

The catalytic hydrogenation of aromatic nitro compounds containing multiple functional groups into amino compounds with high conversion rates, selectivity, and stability under mild conditions is a great challenge. Herein, a well defined catalyst (Co@NC) is prepared through the pyrolysis of the Co-centered metal–organic framework (MOF) at the optimized temperature. The as-synthesized catalyst exhibits a high conversion rate and selectivity for the hydrogenation of 12 aromatic nitro compounds with different competing groups into desired amino compounds with hydrazine hydrate under mild conditions (80 °C, 30 min, and 1 atm). The catalyst also shows excellent stability and can be reused over 20 times without considerably losing its activity. It is found that the Co–Nx site is the main active site for catalytic hydrogenation, and the Mott–Schottky effect between the surface Co NPs and N-doped carbon can further promote the hydrogenation reaction. EXAFS, TEM, XPS, and Raman analyses confirm that cobalt nanoparticles (NPs) are properly encapsulated by the N-doped carbon matrix at the optimized temperature, and the Co species maintain a high spin state after the catalysis, which may be responsible for the high performance of Co@NC. This work demonstrates not only a highly efficient catalyst for hydrogenation under mild conditions, but also provides insight into the active sites in Co-based catalysts for hydrogenation. [ABSTRACT FROM AUTHOR]

Gamma valerolactone (GVL) is an important chemical feedstock from which several value-added fine chemicals, fuels and fuel additives are manufactured. GVL is the product obtained in the hydrogenation of levulinic acid (LA), which in turn is generally manufactured from several renewable resources such as pentoses and hexoses. The present work deals with the synthesis of SBA-15 and Sn loaded catalysts [x% Sn/Al-SBA-15 (x = Si/Sn = 10, 25, 50, 75 and 100 with Si/Al = 25)] using a hydrothermal in situ method. A variety of both bulk and surface characterization techniques such as XRD, FT-IR, BET, FE-SEM, HR-TEM, XPS, TGA/DTA and UV-DRS were used to characterize the bare and Sn/Al-SBA-15 catalysts. The characterization studies revealed the presence of Sn species well dispersed in the uniform pore channels of Al-SBA-15. All the synthesized catalysts were tested in the liquid-phase catalytic transfer hydrogenation of levulinic acid at atmospheric N2 pressure under mild reaction conditions. Among them, the Sn/Al-SBA-15 (Si/Sn = 25) catalyst showed remarkable conversion of levulinic acid (99%) and very high selectivity towards GVL (100%). The various reaction parameters such as metal loading, reaction temperature, reaction time and catalyst weight were optimized to get the maximum conversion of levulinic acid with high selectivity towards the desired product. The stability and reusability of the best catalysts were also tested up to five cycles and there was not much variation in the catalytic activity in terms of conversion. [ABSTRACT FROM AUTHOR]

Carbon-encapsulated Fe3O4 (Fe3O4@C) catalysts were prepared by a solvothermal method using glucose as the carbon source and their physicochemical properties were characterized via various analytical techniques. Catalytic transfer hydrogenation of furfural over Fe3O4@C catalysts was investigated with isopropanol as the solvent and hydrogen donor. The Fe3O4@C catalysts exhibited high catalytic furfural transfer hydrogenation activity, selectivity of furfuryl alcohol, and high reusability. The mechanism of catalytic transfer hydrogenation of furfural by Fe3O4@C obeys the Meerwein–Ponndorf–Verley reduction on a Lewis acid site (Fe3O4). [ABSTRACT FROM AUTHOR]

Developing a highly active, acid-resistant and low-cost catalyst which can perform well in aqueous solution has long been sought for practical and sustainable lignocellulosic biomass transformation. In this work, a series of Ce–P–Co heterogeneous catalysts were prepared by a convenient solvothermal method for catalytic hydrogenation of levulinic acid (LA) to gamma-valerolactone (GVL) in water. By comprehensive characterizations and catalytic measurements, the structure of the prepared Ce–P–Co samples was disclosed as (CePO4)m/Co2P composites with a modulated molar ratio (m) of 0.04–0.34. With the introduction of CePO4, the unique hydrogen activation on CePO4 markedly accelerated the reaction, with the GVL yield after 90 min on (CePO4)m/Co2P (45–97%) being much higher than on pure Co2P (26%), together with an attractive TOF of 0.27–0.61 s−1 on (CePO4)m/Co2P (comparable to precious metal catalysts). Further analysis of the kinetic and acidic features indicated a Langmuir–Hinshelwood mechanism, initiated by activation of H2 and LA on CePO4 and Co2P, respectively, followed by a surface reaction of the two activated species as the rate-determining step, as a plausible pathway for producing GVL from LA on (CePO4)m/Co2P. The consistent catalytic performance during recycling tests and the unchanged morphological, bulk and surface structure features of the used catalyst relative to the fresh catalyst confirmed that the (CePO4)m/Co2P structure was robust enough to endure the acidic aqueous environment for efficiently and sustainably converting LA to GVL. The advantages of high catalytic efficiency, stable, acid-resistant structure and low cost marked (CePO4)m/Co2P as a competitive and practical heterogeneous catalyst for sustainable, scaled-up lignocellulosic biomass transformation. [ABSTRACT FROM AUTHOR]

Metal–ligand cooperativity (MLC) is an established strategy for developing effective hydrogenation and dehydrogenation catalysts. Metal–metal cooperativity (MMC) in bimetallic complexes is not as well understood, and to date has had limited implementation in (de)hydrogenation. Herein we use (de)hydrogenation processes as a platform to examine modes of cooperativity, with a particular focus on catalytic mechanisms. We investigate how lessons learnt from the extensive development of metal–ligand cooperative catalysts can aid the ongoing development of metal–metal cooperative catalysts. [ABSTRACT FROM AUTHOR]