Fractionation of Lignocellulosic Biomass over Core–Shell Ni@Al₂O₃ Catalysts with Formic Acid as a Cocatalyst and Hydrogen Source

Abstract

Highly dispersed, core–shell Ni@Al2O3 on activated carbon (AC) catalysts were prepared to develop an effective, external‐hydrogen‐free fractionation process for various types of lignocellulosic biomass. In a mixture of formic acid, ethanol, and water at 190 °C, the conversion of oak wood produced 23.4 C% lignin‐derived phenolic monomers (LDPMs) and highly delignified pulp‐rich solid. At an early stage, formic acid acted as a cocatalyst to enhance the delignification by solvolysis, and at a later stage, it acted as a hydrogen source to stabilize the phenolic monomers by hydrodeoxygenation and hydrogenation. Based on the positive correlation between spillover hydrogen on the catalysts and LDPM yields, a new suite of catalyst design criteria was proposed to develop highly active, non‐noble‐metal based catalysts for realizing economically viable biorefineries. Enzymatic saccharification of the pulp‐rich solid indicated that the pulp‐rich solid is an excellent source of fermentable sugars.

Liquid Organic Hydrogen Carriers (LOHCs) as H‐Source for Bio‐Derived Fuels and Additives Production

“…[272,273] Under the catalyzed hydroliquefaction conditions, the temperature can be reduced down to 150 °C. [250,257,271] Small molecule alcohols are generally used to extract lignin from biomass feedstock, though they are good solvents also for the liquefaction processes. Moreover, they can act as capping agent to suppress re-polymerization as well as in situ hydrogen donor both via catalytic reforming (MeOH) or catalytic H-transfer (i-PrOH).…”

“…[ 272,273 ] Under the catalyzed hydroliquefaction conditions, the temperature can be reduced down to 150 °C. [ 250,257,271 ]…”

“…The introduction of metal-based catalysts in FA-assisted lignin reductive depolymerization is a useful tools to accelerate the HDO process minimizing the coke production via re-polymerization. [263] When FA is used as H-source, the typically employed metal catalysts are Pd, [264] Pt, [265] Ru, [252,263,[266][267][268] Rh, [269] monometallic Ni [250,251,270,271] catalysts and bimetallic Ni-Mo. [272,273] Under the catalyzed hydroliquefaction conditions, the temperature can be reduced down to 150 °C.…”

Development of ‘Lignin-First’ Approaches for the Valorization of Lignocellulosic Biomass

“…The high yield was explained by transfer hydrogenolysis reactions of lignin fragments targeting the β-O-4′ bond and stabilizing reactive intermediates due to the cobalt catalyst [ 80 ]. Formic acid was also used as hydrogen source and as co-catalysts beside Ni-Al/C in another paper and a positive correlation was suggested between spillover hydrogen on the catalysts and lignin-derived phenolic monomer yields [ 81 ]. Pt/Al 2 O 3 not only converted birch into phenolic monomers but also catalyzed methanol reforming in methanol-water mixtures to supply hydrogen.…”

Utility of Core–Shell Nanomaterials in the Catalytic Transformations of Renewable Substrates

“…Indeed, the yield of phenolic monomers, that is,4 -n-propyl-guaiacol, 4-n-propenyl-guaiacol, 4-n-propyl-syringol, and 4-n-propenyl-syringol, obtained with the Ni/Al 2 O 3 core-shell catalyst is much higher than that obtainedw ith Ni immobilizedo na ctivatedc arbon withouta core-shell structure. [63] Note that in reductivec atalytic fractionation the lignin structure is initially broken down into small fragments by solvolysis,s ometimes termed lignin oil, and the catalysti sr esponsible for hydrogenolysis and hydrogenation of these fragments, which are sufficiently small to pass through the mesoporous catalystshell.…”