Highly Selective Hydrodeoxygenation of Lignin to Naphthenes over Three-Dimensional Flower-like Ni2P Derived from Hydrotalcite

Catalytic Refining Lignin-Derived Monomers: Seesaw Effect between Nanoparticle and Single-Atom Pt

Pt automatically adsorbed on oxygen vacancy of TiO2 via an in situ interfacial redox reaction, resulting in atomically dispersion of Pt on TiO2. In the upgrading of lignin-derived 4-propylguaiacol, single-atom catalyst (SAC) Pt/TiO2-H achieved a conversion of 96.9 % and a demethoxylation selectivity of 93.3 % under 3 MPa H2 at 250 °C for 3 h, markedly different from the performance of nanoparticle counterpart that gave deep deoxygenation selectivity over 99.0 %. The high demethoxylation activity of SAC Pt/TiO2-H is mainly attributed to its weak hydrogen spillover capacity that suppressed the benzene ring hydrogenation and the deep deoxygenation. Additionally, SAC Pt/TiO2-H reduced the energy barrier of CAr-OCH3 bond cleavage and accordingly lowered the Gibbs free energy of the demethoxylation reaction. This facile method could fabricate single-atom Au, Pd, Ir, and Ru supported on TiO2-H, demonstrating the generality of this strategy for the establishment of a library of SACs. Moreover, SAC exhibited versatile capacity in demethoxylation of different lignin-derived monomers and high stability. This study showcases the superiority of atomically dispersed metal catalysts for selective demethoxylation reactions and proposes a renewable alternative to fossil-based 4-alkylphenols through upgrading of lignin-derived monomers.

Structural Ni0-Niδ+ Pair Sites for Highly Active Hydrogenation of Nitriles to Primary Amines

Supported metal pair sites have sparked interest due to their tremendous potential as bifunctional catalysts. Here, we report the structural Ni0-Niδ+ pair sites constructed in a well-defined nanocrystal phase of Ni3P. These Ni0-Niδ+ pair sites exhibited a remarkable product formation rate of 123 molBA/molmetal/h for the hydrogenation of benzonitrile (BN) to benzylamine (BA). The heterogeneity of surface Ni atoms over the Ni3P crystal created two types of metal centers, Ni0 and Niδ+, with a specific spatial distance of 4-5 Å. The Ni0 site acted as the center for H2 activation, while the Niδ+ site served as the adsorption and activation center for the C ≡ N group. The highly efficient cooperation effect of Ni0-Niδ+ pair sites resulted in a TOF of 2915 h-1 in BN hydrogenation, which is 2.4 and 9.7 times higher than that over the mono-Ni0 and -Niδ+ sites, respectively.

Chemiresistive effect of p-type delafossite CuScO2 microsheets to gaseous alcohols

The chemiresistive effect of an oxide significantly influences its electrical properties, which depend greatly on the interactions between the ambient gas molecules and the solid surface, including the gas adsorption and charge transfer still challenging to be clarified. In this work, we investigate the chemiresistive effect of the p-type delafossite CuScO2 microsheets by comparing their responses to various gaseous alcohols, which increase with an approximately linear relationship with the length of straight carbon chains from methanol to n-hexanol. A new mechanism is proposed to elucidate such a dramatic trend of observed chemiresistive change based on the first-principles calculations and test results. The increasing carbon chain length modulates the adsorption configuration and provides supplementary routes for electron transfer, which is assumed to account for the observed chemiresistive effect. This work may provide a novel perspective for the investigation and development of more advanced functional oxides for electrical applications.

Selective production of high-value fuel via catalytic upgrading of bio-oil over nitrogen-doped carbon-alumina hybrid supported cobalt catalysts

Bio-oil derived from biomass fast pyrolysis can be upgraded to gasoline and diesel alternatives by catalytic hydrodeoxygenation (HDO). Here, the novel nitrogen-doped carbon-alumina hybrid supported cobalt (Co/NCAn, n = 1, 2.5, 5) catalyst is established by a coagulation bath technique. The optimized Co/NCA2.5 catalyst presented 100 % conversion of guaiacol, high selectivity to cyclohexane (93.6 %), and extremely high deoxygenation degree (97.3 %), respectively. Therein, the formation of cyclohexanol was facilitated by stronger binding energy and greater charge transfer between Co and NC which was unraveled by density functional theory calculations. In addition, the appropriate amount of Lewis acid sites enhanced the cleavage of the C-O bond in cyclohexanol, finally resulting in a remarkable selectivity for cyclohexane. Finally, the Co/NCA2.5 catalyst also exhibited excellent selectivity (93.1 %) for high heating value hydrocarbon fuel in crude bio-oil HDO. This work provides a theoretical basis on N dopants collaborating alumina hybrid catalysts for efficient HDO reaction.

Transition metal phosphides: synthesis nanoarchitectonics, catalytic properties, and biomass conversion applications

Developing inexpensive and efficient catalysts for biomass hydrogenation or hydrodeoxygenation (HDO) is essential for efficient energy conversion. Transition metal phosphides (TMPs), with the merits of abundant active sites, unique physicochemical properties, tunable component structures, and excellent catalytic activities, are recognized as promising biomass hydrogenation or HDO catalytic materials. Nevertheless, the biomass hydrogenation or HDO catalytic applications of TMPs are still limited by various complexities and inherent performance bottlenecks, and thus their future development and utilization remain to be systematically sorted out and further explored. This review summarizes the current popular strategies for the preparation of TMPs. Subsequently, based on the structural and electronic properties of TMPs, the catalytic activity origins of TMPs in biomass hydrogenation or HDO is elucidated. Additionally, the application of TMPs in efficient biomass hydrogenation or HDO catalysis, as well as highly targeted multiscale strategies to enhance the catalytic performance of TMPs, are comprehensively described. Finally, large-scale amplification synthesis, rational construction of TMP-based catalysts and in-depth study of the catalytic mechanism are also mentioned as challenges and future directions in this research field. Expectedly, this review can provide professional and targeted guidance for the rational design and practical application of TMPs biomass hydrogenation or HDO catalysts.

Reversal Effect of Phosphorus on Catalytic Performances of Supported Nickel Catalysts in Reductive Amination of 1,6-Hexanediol

The reductive amination of 1,6-hexanediol with ammonia is one of the most promising green routes for synthesis of 1,6-hexanediamine. Herein, we developed a phosphorous modified Ni catalyst of Ni-P/Al2O3. It presented satisfactory improved selectivity to 1,6-hexanediamine in the reductive amination of 1,6-hexanediol compared to the Ni/Al2O3 catalyst. The phosphorous tended to interact with Al2O3 to form AlPOx species, induced Ni nanoparticle to be flatter, and the decrease of strong acid sites, the new-formed Ni-AlPOx-Al2O3 interface and the flatter Ni nanoparticle were the key to switch the dominating product from hexamethyleneimine to 1,6-hexanediamine. This work develops an efficient catalyst for production of 1,6-hexanediamine from the reductive amination of 1,6-hexanediol, and provides a point of view about designing selective non-noble metal catalysts for producing primary diamines via reductive amination of diols.

Production of Renewable Hydrocarbon Biofuels with Lignocellulose and Its Derivatives over Heterogeneous Catalysts

In recent years, the issues of global warming and CO2 emission reduction have garnered increasing global attention. In the 21st Conference of the Parties (convened in Paris in 2015), 179 nations and the European Union signed a pivotal agreement to limit the global temperature increase of this century to well below 2 K above preindustrial levels. To fulfill this objective, extensive research has been conducted to use renewable energy sources as potential replacements for traditional fossil fuels. Among them, the production of hydrocarbon transportation fuels from CO2-neutral and renewable biomass has proven to be a particularly promising solution due to its compatibility with existing infrastructure. This review systematically summarizes research progress in the synthesis of liquid hydrocarbon biofuels from lignocellulose during the past two decades. Based on the chemical structure (including n-paraffins, iso-paraffins, aromatics, and cycloalkanes) of hydrocarbon transportation fuels, the synthesis pathways of these biofuels are discussed in four separate sections. Furthermore, this review proposes three guiding principles for the design of practical hydrocarbon biofuels, providing insights into future directions for the development of viable biomass-derived liquid fuels.

Synthesis of P-(NiCo)CO3 /TiO2 /Ti Self-Supported Electrode with High Catalytic Activity and Stability for Hydrogen Evolution

Hydrogen is considered an ideal clean energy due to its high mass-energy density, and only water is generated after combustion. Water electrolysis is a sustainable method of obtaining a usable amount of pure hydrogen among the various hydrogen production methods. However, its development is still limited by applying expensive noble metal catalysts. Here, the dissolution-recrystallization process of TiO2 nanotube arrays in water with the hydrothermal reaction of a typical nickel-cobalt hydroxide synthesis process followed by phosphating to prepare a self-supported electrode with (NiCo)CO3 /TiO2 heterostructure named P-(NiCo)CO3 /TiO2 /Ti electrode is combined. The electrode exhibits an ultra-low overpotential of 31 mV at 10 mA  cm-2 with a Tafel slope of 46.2 mV dec-1 in 1 m KOH and maintained its stability after running for 500 h in 1 m KOH. The excellent catalytic activity can be attributed to the structure of nanotube arrays with high specific surface area, superhydrophilicity, and super aerophobicity on the electrode surface. In addition, the uniform (NiCo)CO3 /TiO2 heterostructure also accelerates the electron transfer on the electrode surface. Finally, DFT calculations demonstrate that phosphating also improves the ΔGH* and ΔGH2O of the electrode. The synthesis strategy also promotes the exploration of catalysts for other necessary electrocatalytic fields.

Interfacial nanoarchitectonics of nickel phosphide supported on activated carbon for transfer hydrogenation of nitroarenes under mild conditions

Metal phosphides are promising catalysts for hydrogenation reactions due to their unique ability to generate active hydrogen species which are essential for desired reactions. In this work, the hydrogenation potential of nickel phosphide (Ni2P) is explored for the transfer hydrogenation of aromatic nitro compounds using hydrazine hydrate as hydrogen source. The Ni2P was supported on activated carbon (AC) to facilitate highly exposed active reaction sites. The as-synthesized Ni2P-AC catalyst showed excellent catalytic potential for the hydrogenation of nitro compounds to corresponding amines with 100% conversion efficiency and resulted in excellent yields. The reaction conditions were optimized by varying different reaction parameters, such as time, temperature, solvents, catalyst amount and hydrogen sources. The developed reaction protocol is highly selective for nitro compounds having reduction susceptible functional groups like -Cl, -Br, -CHO, etc. The structure-activity relationship of the Ni2P-AC was also examined which suggested that both acidic and basic sites present in Ni2P-AC catalyst plays crucial role in hydrogenation reaction. Besides, an in-depth insight into the reaction mechanism illustrates that the reaction proceeds via N-phenyl hydroxylamine as the reaction intermediate. In addition, decent recyclability and stability of Ni2P-AC catalyst demonstrates its highly versatile nature for potential large-scale applications. The use of highly efficient Ni2P-AC catalyst for hydrogenation reactions can lead the way towards sustainable and effective industrial organic catalysis.

Ni12P5 Confined in Mesoporous SiO2 with Near-Unity CO Selectivity and Enhanced Catalytic Activity for CO2 Hydrogenation

CO2 hydrogenation via the reverse water gas shift (RWGS) reaction is a promising strategy for CO2 utilization while constructing Ni-based catalysts with high catalytic activity and perfect CO selectivity remains a great challenging. Here, we demonstrate that the product selectivity for CO2 hydrogenation can be significantly tuned from CH4 to CO by phosphating of SiO2-supported Ni catalysts due to the geometric effect. Interestingly, nickel phosphide catalysts with different crystalline phases (Ni12P5 and Ni2P) differ sharply in CO2 conversion, and Ni12P5 is remarkably more active. Furthermore, we developed a facile strategy to confine small Ni12P5 nanoparticles in mesoporous SiO2 channels (Ni12P5@SBA-15). Enhanced activity is exhibited on Ni12P5@SBA-15, ascribed to the highly effective confinement effect. The in situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculations unveil that catalytic CO2 hydrogenation follows a direct CO2 dissociation route with adsorbed CO as the key intermediate. Notably, strong multibonded CO (threefold and bridge-bonded CO) is feasibly formed on the Ni catalyst accounting for CH4 as the dominant product whereas only weak linearly bonded CO exists on nickel phosphide catalysts resulting in almost 100% CO selectivity. The present results indicate that Ni12P5@SBA-15 combining the geometric effect and the confinement effect can achieve near-unity CO selectivity and enhanced activity for CO2 hydrogenation.

Transition Metal Phosphide Nanoarchitectonics for Versatile Organic Catalysis

Transition metal phosphides (TMP) posses unique physiochemical, geometrical, and electronic properties, which can be exploited for different catalytic applications, such as photocatalysis, electrocatalysis, organic catalysis, etc. Among others, the use of TMP for organic catalysis is less explored and still facing many complex challenges, which necessitate the development of sustainable catalytic reaction protocols demonstrating high selectivity and yield of the desired molecules of high significance. In this regard, the controlled synthesis of TMP-based catalysts and thorough investigations of underlying reaction mechanisms can provide deeper insights toward practical achievement of desired applications. This review aims at providing a comprehensive analysis on the recent advancements in the synthetic strategies for the tailored and tunable engineering of structural, geometrical, and electronic properties of TMP. In addition, their unprecedented catalytic potential toward different organic transformation reactions is succinctly summarized and critically analyzed. Finally, a rational perspective on future opportunities and challenges in the emerging field of organic catalysis is provided. On the account of the recent achievements accomplished in organic synthesis using TMP, it is highly anticipated that the use of TMP combined with advanced innovative technologies and methodologies can pave the way toward large scale realization of organic catalysis.

Boosting Hydrolysis of Cellulose at High Temperature by β-Glucosidase Induced Metal-Organic Framework In-Situ Co-Precipitation Encapsulation

Due to the poor enzyme thermal stability, the efficient conversion of high crystallinity cellulose into glucose in aqueous phase over 50 °C is challenging. Herein, an enzyme-induced MOFs encapsulation of β-glucosidase (β-G) strategy was proposed for the first time. By using various methods, including SEM, XRD, XPS, NMR, FTIR and BET, the successful preparation of a porous channel-type flower-like enzyme complex (β-G@MOFs) was confirmed. The prepared enzyme complex (β-G@MOFs) materials showed improved thermal stability (from 50 °C to 100 °C in the aqueous phase) and excellent resistance to ionic liquids (the reaction temperature was as high as 110 °C) compared to the free enzyme (β-G). Not only the catalytic hydrolysis of cellulose by single enzyme (β-G) in ionic liquid was realized, but also the high-temperature continuous reaction performance of the enzyme was significantly improved. Benefiting from the significantly improved heat resistance, the β-G@MOFs exhibited 32.1 times and 34.2 times higher enzymatic hydrolysis rate compared to β-G for cellobiose and cellulose substrates, respectively. Besides, the catalytic activity of β-G@MOFs was retained up to 86 % after five cycles at 110 °C. This was remarkable because the fixation of the enzyme by the MOFs ensured that the folded structure of the enzyme would not expand at high temperatures, allowing the native conformation of the encapsulated protein well-maintained. Furthermore, we believe that this structural stability was caused by the confinement of flower-like porous MOFs.

Transition Metal Phosphides (TMP) as a Versatile Class of Catalysts for the Hydrodeoxygenation Reaction (HDO) of Oil-Derived Compounds

Hydrodeoxygenation (HDO) reaction is a route with much to offer in the conversion and upgrading of bio-oils into fuels; the latter can potentially replace fossil fuels. The catalyst’s design and the feedstock play a critical role in the process metrics (activity, selectivity). Among the different classes of catalysts for the HDO reaction, the transition metal phosphides (TMP), e.g., binary (Ni2P, CoP, WP, MoP) and ternary Fe-Co-P, Fe-Ru-P, are chosen to be discussed in the present review article due to their chameleon type of structural and electronic features giving them superiority compared to the pure metals, apart from their cost advantage. Their active catalytic sites for the HDO reaction are discussed, while particular aspects of their structural, morphological, electronic, and bonding features are presented along with the corresponding characterization technique/tool. The HDO reaction is critically discussed for representative compounds on the TMP surfaces; model compounds from the lignin-derivatives, cellulose derivatives, and fatty acids, such as phenols and furans, are presented, and their reaction mechanisms are explained in terms of TMPs structure, stoichiometry, and reaction conditions. The deactivation of the TMP’s catalysts under HDO conditions is discussed. Insights of the HDO reaction from computational aspects over the TMPs are also presented. Future challenges and directions are proposed to understand the TMP-probe molecule interaction under HDO process conditions and advance the process to a mature level.

Effect of P on hydrodeoxygenation performance of Ni–P/SiO2 catalysts for upgrading of m-cresol

Ni–P/SiO2-1.0 exhibited much higher MCH selectivity than Ni/SiO2, which is due to the increase in acidity caused by the introduction of P.