Table 32. Overview of the Reductive Catalytic Fractionation of Biomass to Alkyl Phenolics.

Entry	Source and scale	Catalyst and cat.:substrate ratio	Setup	Solvent	Conditions	Total monomer yield	Major products	Carbohydrate retention	Year and ref
1	Birch; 4 g	Pt/C, Pd/C, Ru/C, Rh/C and 1% H3PO4; 0.075:1	Batch reactor	1,4-dioxane/H2O (1:1, v/v)	200 °C, H2 4 MPa, 4 h	Up to 46.4%	4-n-Propanol-guaiacol/syringol	Not reported	2008 (672)
2	Pine, 2.2 g	Pd/C; 0.08:1	Batch reactor	1,4-dioxane/water (1:1 v/v)	195 °C, H2 3.45 MPa, 24 h	22.0%	4-n-Propyl-guaiacol and 4-n-propanolguaiacol	Not reported	2011713
3	Birch, corn stalk, pine, poplar, beech, etc.; 1 g	Ni-W2C/AC Na2SO4 and NaCl could be added; 0.4:1	Batch reactor	H2O	235 °C, H2 6 MPa, 4 h	Up to 46.5%	4-n-Propyl-guaiacol/syringol	Converted to diols; total yield up to 76.1% and mainly ethylene glycol	2012 (674)
4	Birch; 2 g	Ni/C; 0.05:1	Batch reactor	MeOH	200 °C, Ar 0.1 MPa, 6 h	48.6%	4-n-Propyl-guaiacol/syringol	Not reported	2013 (675)
5	Poplar; 16 g	Raney Ni; 0.625:1	Batch reactor	2-PrOH/H2O (7:3, v/v)	180 °C, Ar 0.1 MPa, 3 h	25% bio-oil based on initial weight of biomass	Mostly alkylphenolics as shown by 2D-GC	71%	2014 (676)
6	Birch; 10 g	Pd/C; 0.13:1	Batch reactor	Ethanol/H2O (1:1, v/v)	195 °C, Ar 0.4 MPa, 1 h	49% isolated yield	2,6-Dimethoxy-4-(prop-1-enyl)-phenol	Not reported	2014 (679)
7	Poplar; 1 g	ZnPd (1:0.1)/C	Batch reactor	MeOH	220 °C, H2 3.4 MPa, 12 h	Up to 54%	4-n-prolyl-guaiacol/syringol	74%	2014 (681)
8	Birch; 2 g	Ru/C; 0.15:1	Batch reactor	MeOH	250 °C, H2 3 MPa, 3–6 h	Up to 52% monophenols	4-n-prolyl-guaiacol/syringol in 41%	92%	2015 (683)
9	Pine, corn stalk, corncob, wheat straw, rice straw; 1 g	Ru/C + LiTaMo6; 0.2:0.2:1	Batch reactor	Aqueous H3PO4 solution (0.1–0.3 M)	230 °C, H2 6 MPa, 24 h	Up to 35.4% phenols	Mostly alkylphenolics	Converted to gasoline alkanes with the yield up to 82.4%	2015 (714)
10	Birch; 2 g	Ru/C and Pd/C; 0.2:1	Batch reactor	MeOH	250 °C, H2 3 MPa, 3 h	48% and 49% for Ru/C and Pd/C, respectively	Selectivity change from 4-n-prolyl-guaiacol/syringol (75%) to 4-n-propanol-guaiacol/syringol (91%)	85% and 89% for Ru/C and Pd/C, respectively	2015 (715)
11	Miscanthus; 1 g	Ni/C; 0.15:1	Batch reactor	MeOH	225 °C, H2 3.5 MPa, 12 h	68%	Methyl dihydroferulate and methyl p-hydroxyhydrocinnamate in 28%; 4-n-prolylguaiacol/syringol in 40%	88.5%; further converted to furfural and levulinic acid	2016 (682)
12	Corn stover; 1 g	Ru/C, Ni/C; 0.1:1	Batch reactor	MeOH	200–250 °C, H2 3 MPa, 1–6 h	Up to 38% monophenolic monomers	65% selectivity to methyl coumarate/ferulate	>90%	2016 (716)
13	Poplar; 2 g	Pd/C; 0.1:1	Batch reactor	MeOH with H3PO4 or NaOH at 1.25–5 g/L	200 °C, H2 2 MPa, 3 h	Up to 42% monophenols	35% 4-n-Propanolsyringol	Approximately 65–90%	2016 (685)
14	Poplar; 2 g	Pd/C; 0.1:1	Batch reactor	MeOH or EtOH with varying water content from 0 to 100%	200 °C, H2 2 MPa, 3 h	Up to 45% monophenols	4-n-Propanol-guaicol/syringol as major products	Up to 98%	2016 (686)
15	Birch, poplar, spruce, pine; 10 g	Pd/C; 0.1:1	Batch reactor	Ethanol–water (1:1, v/v)	210 °C, 15 h	Up to 36% monophenolics	4-n-Propyl/propenyl-syringol as major products	Up to 64%	2016 (666)
16	Beech; 1 g	Ni/C; 0.1:1	Batch reactor	MeOH–water (6:4, v/v)	200 °C, H2 2 MPa, 5 h	Up to 51.4%	75.3% selectivity to 4-n-propanol-guaiacol/syringol	Not reported	2016 (717)
17	Birch, oak, Douglas fir; 2 g	Pd/C+Al(OTf)3; 0.1:1HCl; H2SO4, H3PO4, CH3COOH; p-TsOH was also tested as co-catalyst	Batch reactor	MeOH	180 °C, H2 3 MPa, 2 h	Up to 48% monophenolics	Mixture of alkylmethoxyphenols	Up to 96%	2016, 2017, 2018697−700
18	Birch; 2 g	Ni/Al2O3 in basket; 0.1:1	Batch reactor	MeOH	250 °C, H2 3 MPa, 3 h	More than 40% monophenols	70% selectivity to 4-n-propanol-guaiacol/syringol	93% glucose and 83% xylose retention	2017 (688)
19	Eucalyptus; 2 g	Ru/C; 0.1:1	Batch reactor	n-Butanol/water (1:1, v/v)	200 °C, H2 3 MPa, 3 h	Up to 50% monophenols	4-n-Propanol-guaiacol/syringol as major products	Hemicellulose to polyols with yield of 49%; cellulose 96% yields as pulp	2018 (689)
20	Pine, walnut, poplar, oak, beech, etc.; 1 g	Cu20-PMO; 0.2:1	Batch reactor	MeOH	180 °C, H2 4 MPa, 18 h	Up to 36%	4-n-Propanolguaiacol/syringol were isolated at yield of with selectivity of 67%	to aliphatic alcohols at elevated conditions (320 °C, 6 h)	2018 (703)
21	Birch; 0.2 g	Cobalt on phenanthroline/carbon catalyst (Co-phen/C); 0.15:1	Batch reactor	EtOH/H2O (1:1, v/v) and HCOOH + HCOONa as hydrogen donor	200 °C, 4 h	34%	56% selectivity to 4-n-propyl/propenyl-syringol	32%	2018 (680)
22	Apple wood, pine; 0.5 g	MoxC/CNTs for hardwood; Ru/CMK-3 for softwood and grass	Batch reactor	MeOH	250 °C, H2 1 MPa, 3 h	Up to 42% monophenolics for hard wood, 20% for soft wood	Mostly alkylphenolics	For Mo-based cat. C5 and C6, retention of 89 and 98%, respectively; for Ru-based cat., 52.9%	2018 (718)
23	Birch; 2 g	Pt/γ-Al2O3; 0.25:1	Batch reactor	MeOH/water (1:2, v:v)	230 °C, N2 3 MPa, 3 h	49.5% monophenolics	46.1% Propylguaiacol/syringol	41%	2019 (719)
24	Beech; 1 g	Pd70Pt30 NPs	Batch reactor	MeOH	250 °C, H2 3 MPa, 3 h	45%	Sum of 4-n-propyl-guaiacol/syringol and 4-n-propanol-guaiacol/syringol	Not reported	2019 (720)
25	Pine; 1 g	α-HfP NPs; 0.2:1	Batch reactor	H2O	190 °C, H2 3.5 MPa, 3 h	19.8%	18.5% 4-n-Propylguaiacol	Not reported	2019 (504)
26	Eucalyptus; 0.5 g	Ni@ZIF-8; 0.1:1	Batch reactor	MeOH	260 °C, H2 3 MPa, 8 h	44.3%	55% selectivity to 4-n-propyl-guaiacol/syringol	Not reported	2019 (721)
27	Eucalyptus; 1 g	Pd/C; 0.1:1	Batch reactor	MeOH	240 °C, H2 3 MPa, 4 h	49.8 wt%	4-n-Propanolguaiacol 12.9% and 4-n-propanolsyringol 31.9%	Retention C5 of 67.8% and C6 of 82.5%; to furfural catalyzed by FeCl3 in another step	2020 (722)
28	Birch; 2 g	Ni50Pd50/SBA-15; 0.075:1	Batch reactor	i-PrOH:H2O (2:1, v/v)	245 °C, N2 1 MPa, 4 h	37.2%	18.9% 4-n-Propylsyringol	Not reported	2020 (723)
29	Hemp hurd; 0.2 g	Pd/C; 0.1:1	Batch reactor	MeOH/H2O (7:3, v:v)	200 °C, 4 h	38%	High selectivity to 4-n-propyl/propanolsyringol	Approximately 43%	2021 (724)
30	Corn stover; 1 g	Co/AC-N; 0.1:1	Batch reactor	i-PrOH/water/ formic acid (10:1:1, v:v:v)	235 °C, N2 0.1 MPa, 200 min	24%	High selectivity to 4-n-ehtylguaiacol and 4-n-ethylphenol	8%	2021725
31	Triploid poplar; 0.5 g	Ru/C, Cs2CO3 (4 wt%); 0.1:1	Batch reactor	MeOH	220 °C, H2 3 MPa, 4 h	30.2%	High selectivity to propyl/propanol guaiacol/syringol	Retention of C5 53% and C6 80%	2022 (726)
32	Pine; 10 g	CuO/C; 0.1:1	Batch reactor	MeOH	240 °C, H2 3 MPa, 4 h	12.1% isolated yield	Isolated 4.8% for propylguaiacol and 7.5% for propanolguaiacol	Not reported	2022 (727)
33	Various types of hardwood, softwood, and herbaceous planta; 0.5 g	Ru/CNT; 0.1:1	Batch reactor	MeOH	220 °C, H2 3 MPa, 4 h	Up to 46% in general hardwood > herbaceous plant > softwood	For hard wood, high selectivity to propanol/propylsyringol/guaiacol	Not reported	2022 (728)
34	Poplar; 1 g	Ru/C, Pd/C, Pt/C, Ni/C; 0.1:1	Batch reactor	Ethylene glycol, 1,2-propanediol, 2,3-butanediol, and glycerol	225 °C, 3 h, flushed with He before reaction	Up to 21%	High selectivity to propyl/propanol guaiacol/syringol	Not reported	2023 (695)
35	Poplar; 1 g	0.3 g Ni/C catalyst mixed with SiO2 (50/50) dispersed inSiC	Flow reactor	Methanol with flow rate of 0.5 mL/min	190 °C for both beds, 6 MPa H2 with a flow rate of 50 mL/min, 3 h	Up to 18%	High selectivity to propylguaiacol/syringol	Not reported	2017 (706)
36	Birch; 0.15 g	Pd/C; 0.15 g	Flow reactor	2.8 g L–1 H3PO4 in MeOH–H2O 7:3 v/v; flow rate 0.3 mL/min	Solvolysis bed = 200 °C; catalytic bed = 180 °C, BPR 3 MPa H2, 3 h	37%	71% selectivity toward 4-n-propylguaiacol/syringol and their corresponding methyl ether derivatives	92%	2017 (711)
37	Birch; 1 g	β-zeolite; 2 g	Flow reactor	Ethanol/H2O (9:1, v/v); flow rate 0.5 mL/min	220 °C, 5 MPa, 3 h	16%	Ca. 60% selectivity to unsaturated aromatics, namely eugenol and isoeugenol	Not reported	2021 (708)
38	Poplar; 300 mg	Ru/C; 0.15:1	Batch reactor	2-Butanol 5 mL and 25 wt% aq. NH3 1 mL	255 °C, H2 3 MPa H2, 3 h	65.6% monophenolics	26.6% 4-[3-(2-Butyl)amino]propyl]phenol	C6 98%, C5 86%	2023 (712)