Efficient conversion of lactic acid to alanine over noble metal supported on Ni@C catalysts

Alanine (Ala), regarded as the building block for protein synthesis, has been widely used in the field of food processing, pharmaceutical, and bio-based plastic industries. Containing plenty of oxygenic functional groups, biomass-derived chemicals are proper for Ala synthesis in an economic and green way via amination. In this work, lactic acid (LA) derived from renewable biomass and waste glycerol (the major by-product of biodiesel industry) was used to produce Ala. Here, a series of magnetic catalysts M/Ni@C (M = Ru, Pt, Pd, Ir, and Rh) were synthesized by ethylene glycol reduction of metal M supported on encapsulated Ni@C. Compared with catalysts based on other M metals, Ru/Ni@C catalysts exhibited extraordinary efficiency with 91.4% selectivity for Ala synthesis from LA (63.7% yield of Ala and 69.7% conversion of LA). The results of experiments and catalyst characterization indicated that the doping of M metals could improve the dehydrogenation ability of catalysts, as well as the ability of NH3 adsorption, facilitating the reaction towards Ala. Overall, this study provides an efficient chemo-catalytic way for the production of Ala from biomass-derived substrates

Catalytic Hydrogenolysis of Biomass-derived Polyhydric Compounds to C-2-C-3 Small-Molecule Polyols: A Review

Biomass energy has attracted much attention because of its clean and renewable characteristics. At present, C-2-C-3 polyols such as glycerol, 1,2-propanediol, and ethylene glycol, widely used as platforms for downstream chemicals or directly used as chemicals in diversified industries, mainly depend on the petrochemical industry. In terms of the feedstock for C-2-C-3 polyol production, the C-3-derived glycerol is a side product during biodiesel synthesis, whereas the C-5-derived xylitol and C-6-derived sorbitol can be mainly obtained by hydrolysis-hydrogenation of hemicellulose and cellulose from lignocellulosic biomass, respectively. In this review, we summarize the catalysts and catalysis for selective hydrogenolysis of these polyhydric compounds to C-2-C-3 polyols and introduce the reaction pathways for the target polyol formation based on the C-3, C-5, and C-6 polyhydric alcohol hydrogenolysis. Finally, state-of-the-art technologies are described and the remaining challenges and further prospects are presented in view of the technical aspects

Catalytic Production of Oxygenated and Hydrocarbon Chemicals From Cellulose Hydrogenolysis in Aqueous Phase

As the most abundant polysaccharide in lignocellulosic biomass, a clean and renewable carbon resource, cellulose shows huge capacity and roused much attention on the methodologies of its conversion to downstream products, mainly including platform chemicals and fuel additives. Without appropriate treatments in the processes of cellulose decompose, there are some by-products that may not be chemically valuable or even truly harmful. Therefore, higher selectivity and more economical and greener processes would be favored and serve as criteria in a correlational study. Aqueous phase, an economically accessible and immensely potential reaction system, has been widely studied in the preparation of downstream products of cellulose. Accordingly, this mini-review aims at making a related summary about several conversion pathways of cellulose to target products in aqueous phase. Mainly, there are four categories about the conversion of cellulose to downstream products in the following: (i) cellulose hydrolysis hydrogenation to saccharides and sugar alcohols, like glucose, sorbitol, mannose, etc.; (ii) selective hydrogenolysis leads to the cleavage of the corresponding glucose C-C and C-O bond, like ethylene glycol (EG), 1,2-propylene glycol (PG), etc.; (iii) dehydration of fructose and further oxidation, like 5-hydroxymethylfurfural (HMF), 2,5-furandicarboxylic acid (FDCA), etc.; and (iv) production of liquid alkanes via hydrogenolysis and hydrodeoxygenation, like pentane, hexane, etc. The representative products were enumerated, and the mechanism and pathway of mentioned reaction are also summarized in a brief description. Ultimately, the remaining challenges and possible further research objects are proposed in perspective to provide researchers with a lucid research direction

Ultrafast Glycerol Conversion to Lactic Acid over Magnetically Recoverable Ni-NiOx@C Catalysts

Lactic acid (LA), a key platform chemical from biomass, is an ideal feedstock for biodegradable plastic synthesis. The conversion of glycerol to LA was investigated over graphiticcarbon-layer-encapsulated Ni-NiOx core/shell (Ni-NiOx@C) catalysts, which were prepared by controlled oxidation from pristine Ni@C. The oxidation temperature greatly influenced the percentage of NiOx and thus the amount of Lewis acid. In the conversion of glycerol, the catalyst oxidized at 200 degrees C provided hitherto the highest LA formation rate (5.67 mol/(m(3).g(cat).s)), which is at least 15 times faster than those obtained over the reported Cu and noble metal catalysts under comparable reaction conditions. The excellent performance of Ni-NiOx@C was attributed to the synergistic effect of the homogenous base, metallic Ni, and acidic NiOx sites, which accelerates the bond cleavage of alpha-C-H and C-O and promotes ultrafast formation of LA within 30 min

Selective C-3-C-4 Keto-Alcohol Production from Cellulose Hydrogenolysis over Ni-WOx/C Catalysts

Keto-alcohols, which are traditionally produced from fossil resources with multisteps, are considered as important intermediates for diversified high-value-added fine chemical synthesis due to their involved carbonyl and hydroxyl groups. Herein, direct cellulose hydrogenolysis to C-3-C-4 keto-alcohol products (hydroxyacetone and 1(3)hydroxy-2-butanone) was achieved over Ni-WOx/C catalysts with an W/Ni atom ratio of 1.0-5.0. The keto-alcohol yield was proposed to strongly depend on the W/Ni ratio and the catalyst annealing temperature. The highest keto-alcohol yield of 63% was obtained at the optimal balance of basic/acidic WOx species and metallic Ni. The introduction of Ni facilitated the formation of the basic W5+ sites, which enhanced the formation of basic sites at the Ni-WOx interface. The synergistic effect between the basic W5+ and acidic oxygen vacancy (Vo) could activate the target C-O/C=O bonds, promoting the isomerization of glucose and C-3-C-4 aldehyde intermediates with the assistance of the interfacial Ni. The cooperative adsorption of the -OH and -C=O groups at the Ni-O-W-Vo interface stabilized the adjacent ketone and hydroxyl groups and kept the other hydroxyl groups for hydrogenolysis, obtaining the final C-3-C-4 keto-alcohols. This work expanded the application of cellulosic biomass, enabling the green and sustainable synthesis of the high-value C-3-C-4 keto-alcohol products using lignocellulosic biomass as a raw material

Selective (ligno) cellulose hydrogenolysis to ethylene glycol and propyl monophenolics over Ni-W@C catalysts

The bi-functional Ni-W@C catalysts were prepared by one-pot reduction-carbonization method and used in hydrogenolysis of cellulose as well as raw lignocellulosic biomass to chemicals. The catalytic performance for cellulose conversion showed that it was more favorable for ethylene glycol (EG) production, obtaining the highest EG yield 60.1% over the Ni-W@C(700)catalyst. The Ni-W@C bimetallic catalysts are systematically characterized with BET, XRD, Raman, XPS, TEM techniques and experiments to probe the active catalytic sites of the catalysts. The effects of calcination temperature of Ni-W catalysts, reaction time, temperature and H(2)pressure on cellulose hydrogenolysis were investigated in detail. The Ni particles could lead to produce more W(5+)active sites, which promotes the glucose retro-aldol condensation to break the target C-C bonds. Metallic Ni catalyzed C=O hydrogenation and C-C hydrogenolysis, which could also avoid the coke formation. The EG selectivity was dependent on the synergy of WO(x)and Ni metal sites. In addition, this synergistic effect between the metal and WO(x)could promote lignin component degradation in direct conversion of untreated raw lignocellulosic biomass, obtaining the propyl monophenolics including guaiacylpropane, syringylpropane and p-n-propylphenol with a total yield of 17.3 wt% besides EG