Potential of Staphylea holocarpa Wood for Renewable Bioenergy

Energy is indispensable in human life and social development, but this has led to an overconsumption of non-renewable energy. Sustainable energy is needed to maintain the global energy balance. Lignocellulose from agriculture or forestry is often discarded or directly incinerated. It is abundantly available to be discovered and studied as a biomass energy source. Therefore, this research uses Staphylea holocarpa wood as feedstock to evaluate its potential as energy source. We characterized Staphylea holocarpa wood by utilizing FT–IR, GC–MS, TGA, Py/GC–MS and NMR. The results showed that Staphylea holocarpa wood contained a large amount of oxygenated volatiles, indicating that it has the ability to act as biomass energy sources which can achieve green chemistry and sustainable development.


Introduction
Human civilization has reached a new historical height with current developments in science and technology, but it has also increased its utilization of energy simultaneously. Energy is extremely important for the development of the material basis and society, and is particularly important economically [1]. As an important material base, energy has played an indispensable role in nation building and human development. These include GDP growth, social and scientific development and the security of the nation [2]. At present, most countries in the world are still obtaining most of their energy from fossil energy [3]. However, the drastic reduction in fossil energy and the ecological environment has brought many problems. Therefore, it is necessary to develop renewable energy in order to alleviate the over-consumption of non-renewable energy [4].
Biomass is an important energy source in renewable energy because it can achieve carbon neutrality. Biomass has many advantages, such as diversity, practicality and sustainability [5]. Biomass can be turned into usable energy through a variety of methods, including physical and chemical methods. Examples of biomass include plants, forest waste, animal waste and municipal solid waste, etc. [6]. According to the World Bioenergy Association statistical report, biomass accounted for 9.5% of all energy supply and contributed about 55.6 EJ of energy in 2017. The greatest contribution to bioenergy belongs to the forestry sector, where forestry biomass has contributed up to 85% of the total energy [7,8].

FT-IR Analysis
In this experiment, the FT-IR of four S. holocarpa wood extracts were analyzed in the range of 4000-550 cm -1 (Figure 1). Different functional groups were observed in the fou extracts. All samples showed bands around 3376 cm -1 , indicating tensile vibrations of in termolecular H-O-H [33,34]. The tensile vibrations of -CH2-in alkanes were mainly dis tributed in the range of 2976-2837 cm -1 [35]. Due to the presence of ester acids and aro matic components, there were C=C and C=O stretching at 1655 cm -1 [36]. Bands close to 1927 cm -1 also represent =O stretching, and the high wave number may occur due to th induced effect of C-F substituents. The absorption peaks at 1454, 1414, 1412 and 1380 cm 1 belong to C-H stretching [37]. There is a small absorption peak at 1275 cm -1 in S. holocarp wood ethanol, ethanol/benzene and ethanol/methanol extracts, but not in S. holocarp wood methanol extract, representing -CH3 bonds [38]. Due to -O vibration, there wer overlapping peaks between 1090 and 1115 cm -1 [39]. In particular, the deep bands at 102 cm -1 (A1 extract) and 1051 cm -1 (the other three extracts) indicate -O stretching in the tet rahedral sheet [40]. The formation of peaks at 1090 and 1053 cm -1 was due to C-O-C and -OH vibrations. Thus, -OH, together with the peak assigned to the aromatic ring (1655 cm -1 ), indicates the presence of phenols [41]. All spectra exhibit similar spectral signatures, except for differences in infrared ab sorption intensity. Typical aromatic bands of lignin were at 1655 and 1454 cm -1 (Figure 1 [42]. These samples were rich in carbon, because the transmission intensity of each peak gradually increases as the type of carbon changes. In contrast, the number of absorption peaks in S. holocarpa wood ethanol, ethanol/benzene and ethanol/methanol extracts wer greater than in S. holocarpa wood methanol extract, and absorption peaks were associated with -CH3 bonds [43]. The FT-IR spectrum showed no -C≡C-vibrations at 2140-2100 cm 1 , indicating the absence of a C≡C functional group in S. holocarpa wood ( Figure 1). Anothe possible reason is that during the extraction process, some chemical bonds become unsta ble, or condense under high temperature conditions [44]. In general, the main chemica components of S. holocarpa wood samples characterized by FT-IR testing include phenols All spectra exhibit similar spectral signatures, except for differences in infrared absorption intensity. Typical aromatic bands of lignin were at 1655 and 1454 cm −1 (Figure 1) [42]. These samples were rich in carbon, because the transmission intensity of each peak gradually increases as the type of carbon changes. In contrast, the number of absorption peaks in S. holocarpa wood ethanol, ethanol/benzene and ethanol/methanol extracts were greater than in S. holocarpa wood methanol extract, and absorption peaks were associated with -CH 3 bonds [43]. The FT-IR spectrum showed no -C≡C-vibrations at 2140-2100 cm −1 , indicating the absence of a C≡C functional group in S. holocarpa wood ( Figure 1). Another possible reason is that during the extraction process, some chemical bonds become unstable, or condense under high temperature conditions [44]. In general, the main chemical components of S. holocarpa wood samples characterized by FT-IR testing include phenols, alcohols, acids, and hydrocarbons. The absorption peaks of the four sample extracts were mainly distributed at 3800-3030 cm −1 , 3030-2835 cm −1 , and 1500-881 cm −1 .
In addition, many chemical components that are conducive to the development of biomass energy were detected in the four extracts. For example, furfural is an important biomass-derived platform molecule that can be used to synthesize a variety of valueadded chemicals. Furfural and its derivatives are promising alternatives to traditional petrochemicals [50]. The furfural industry is constantly evolving. Recently, the annual global production of furfural exceeded 300,000 tons, of which about 70% was produced in China [51]. Furfural and its derivatives are widely used in industrial production in organic solvents, pharmaceuticals, agricultural chemicals, biofuels and fuel additives [52]. One of the most important value-added products obtained from glycerin is dihydroxyacetone. Dihydroxyacetone can also be used as a building block in organic synthesis and is a promising area for the development of novel polymer biomaterials. One example is the design of injectable synthetic biodegradable polymer biomaterials composed of polyethylene glycol and a polycarbonate of dihydroxyacetone [53,54]. Among the various biomass-derived chemicals, 5-hydroxymethylfurfural has received great attention due to its potential applications, and is listed by the U.S. Department of energy as a promising platform chemical [55]. 5-hydroxymethylfurfural is a high-value central platform chemical that can be obtained directly from hexose dehydration. The unique structure of 5-hydroxymethylfurfural gives it high chemical activity and allows it to be transformed through various catalytic processes such as oxidation, hydrogenation and amination. It can be used in the production of high value-added chemicals and liquid fuels such as 2,5-furandialdehyde, 2,5-furandicarboxylic acid, levulinic acid, etc. [56]. In general, the chemical components identified via GC-MS from the S. Holocarpa wood extracts shows its potential in biomedicine and bioenergy. Thus, S. Holocarpa wood has the potential to be used as a lignocellulosic biomass source for bioenergy production.

TGA Analysis
The decomposition process of S. holocarpa wood was studied by TGA method in the range of 30-300 • C (rate of 20 • C/min). The changes in sample mass (TGA) and thermal degradation rate (DTG) are shown in Figure 3. According to the TGA curve, there were two distinct heat loss phases in S. holocarpa wood. The first stage occurs at temperatures around 83 • C and the weight of the wood was slightly reduced by 3.33%. As shown in the DTG curve, the maximum mass loss rate for this stage occurs at the first peak of 54 • C. There were reports that this stage was a drying process, where mass loss represents the removal of moisture and volatiles [57]. The weight reduction of S. holocarpa wood (3.33%) indicates that the wood has a certain moisture. The second phase of the mass reduction occurred in the range of 190-300 • C, and the wood mass was reduced by a total of 20.63% [58].
In addition, many chemical components that are conducive to the development of biomass energy were detected in the four extracts. For example, furfural is an important biomass-derived platform molecule that can be used to synthesize a variety of valueadded chemicals. Furfural and its derivatives are promising alternatives to traditional petrochemicals [50]. The furfural industry is constantly evolving. Recently, the annual global production of furfural exceeded 300,000 tons, of which about 70% was produced in China [51]. Furfural and its derivatives are widely used in industrial production in organic solvents, pharmaceuticals, agricultural chemicals, biofuels and fuel additives [52]. One of the most important value-added products obtained from glycerin is dihydroxyacetone. Dihydroxyacetone can also be used as a building block in organic synthesis and is a promising area for the development of novel polymer biomaterials. One example is the design of injectable synthetic biodegradable polymer biomaterials composed of polyethylene glycol and a polycarbonate of dihydroxyacetone [53,54]. Among the various biomass-derived chemicals, 5-hydroxymethylfurfural has received great attention due to its potential applications, and is listed by the U.S. Department of energy as a promising platform chemical [55]. 5-hydroxymethylfurfural is a high-value central platform chemical that can be obtained directly from hexose dehydration. The unique structure of 5-hydroxymethylfurfural gives it high chemical activity and allows it to be transformed through various catalytic processes such as oxidation, hydrogenation and amination. It can be used in the production of high value-added chemicals and liquid fuels such as 2,5-furandialdehyde, 2,5-furandicarboxylic acid, levulinic acid, etc. [56]. In general, the chemical components identified via GC-MS from the S. Holocarpa wood extracts shows its potential in biomedicine and bioenergy. Thus, S. Holocarpa wood has the potential to be used as a lignocellulosic biomass source for bioenergy production.

TGA Analysis
The decomposition process of S. holocarpa wood was studied by TGA method in the range of 30-300 °C (rate of 20 °C/min). The changes in sample mass (TGA) and thermal degradation rate (DTG) are shown in Figure 3. According to the TGA curve, there were two distinct heat loss phases in S. holocarpa wood. The first stage occurs at temperatures around 83 °C and the weight of the wood was slightly reduced by 3.33%. As shown in the DTG curve, the maximum mass loss rate for this stage occurs at the first peak of 54 °C. There were reports that this stage was a drying process, where mass loss represents the removal of moisture and volatiles [57]. The weight reduction of S. holocarpa wood (3.33%) indicates that the wood has a certain moisture. The second phase of the mass reduction occurred in the range of 190-300 °C, and the wood mass was reduced by a total of 20.63% [58]. The decomposition temperature of the wood biomass was about 190 • C; however, this decomposition temperature was delayed compared to some reported plants, such as J. nudiflorum wood biomass [59]. The DTG curve has a peak around 300 • C, indicating Molecules 2023, 28, 299 6 of 17 that weight loss was fastest at this temperature. This stage was the active pyrolysis zone which belongs to the main stage of the volatile stage and pyrolysis mass loss [60]. The mass reduction was mainly due to the breakdown of lignocellulose's organic components. At this stage, the mass changes significantly, possibly caused by the changes in the chemical structure; chemical composition macromolecules were rapidly decomposed into more volatile small molecules at high temperatures [61]. The mass loss in the whole process of 0-300 • C is only 23.96%, and the heat loss is small, indicating that S. holocarpa wood has good thermal stability. In addition, the temperature set by this project was far from the carbonization temperature > 300 • C. Therefore, more volatile components can be obtained using this process [62].
The decomposition temperature of the wood biomass was about 190 °C; however, this decomposition temperature was delayed compared to some reported plants, such as J. nudiflorum wood biomass [59]. The DTG curve has a peak around 300 °C, indicating that weight loss was fastest at this temperature. This stage was the active pyrolysis zone which belongs to the main stage of the volatile stage and pyrolysis mass loss [60]. The mass reduction was mainly due to the breakdown of lignocellulose's organic components. At this stage, the mass changes significantly, possibly caused by the changes in the chemical structure; chemical composition macromolecules were rapidly decomposed into more volatile small molecules at high temperatures [61]. The mass loss in the whole process of 0-300 °C is only 23.96%, and the heat loss is small, indicating that S. holocarpa wood has good thermal stability. In addition, the temperature set by this project was far from the carbonization temperature > 300 °C. Therefore, more volatile components can be obtained using this process [62].

Py/GC-MS Analysis
A total of 214 compounds were identified based on Py/GC-MS results (Figure 4). Among the compounds, the products of S. holocarpa wood pyrolysis at 500 °C were: ethyne, fluoro-(5.96%), dihydroxyacetone (4.22%), acetaldehyde (3.31%), ethyl ether (2.81%), hexadecanenitrile (2.33%), 2-propanone, 1-hydroxy-(2.11%), methyl glyoxal (2.07%), furfuryl alcohol, tetrahydro-5-methyl-, cis-(2.05%), etc. (see Table S5). According to the statistics of Table S5, there are seven categories of ketones (48,20.35%), aldehydes (13, 9.09%), acids (10, 3.09%), esters (18, 6.42%), alcohols (40,15.64%), phenols (18,18.69%), and ethers (5, 0.79%), of which the proportion of ketones (10.31%), alcohols (13.66%) and phenols (27.89%) were higher (Figure 5a). The pyrolysis of S. holocarpa wood is divided into three stages according to the time: <5 min, 5-25 min and >25 min; the pyrolysis products account for 10.795%, 47.546% and 41.695%, respectively (Figure 5b). In the <5 min stage, most of the pyrolysis products were small molecules of organic acids. In the 5-25 min stage, the pyrolysis products were mainly ketone compounds, and the reaction types were mainly double-bond reductions due to the presence of C=C and C=O. Most furan and cyclopentenones come from hemicellulose [63]. In the stage >25 min, the major component was phenolic substances and their derivatives produced by lignin pyrolysis. At the stage of 5-25 min, the pyrolysis products of the sample were the highest, indicating that the ketone content was high [64]. According to the properties of compounds at different stages, most of the compounds identified were organic acids, ketones, furans, cyclopentenes, phenols and their derivatives [65]. Most of these compounds are used in biopharmaceutical, chemical and energy industries [66,67]. According to the statistics of Table S5, there are seven categories of ketones (48,20.35%), aldehydes (13,9.09%), acids (10, 3.09%), esters (18, 6.42%), alcohols (40,15.64%), phenols (18,18.69%), and ethers (5, 0.79%), of which the proportion of ketones (10.31%), alcohols (13.66%) and phenols (27.89%) were higher (Figure 5a). The pyrolysis of S. holocarpa wood is divided into three stages according to the time: <5 min, 5-25 min and >25 min; the pyrolysis products account for 10.795%, 47.546% and 41.695%, respectively (Figure 5b). In the <5 min stage, most of the pyrolysis products were small molecules of organic acids. In the 5-25 min stage, the pyrolysis products were mainly ketone compounds, and the reaction types were mainly double-bond reductions due to the presence of C=C and C=O. Most furan and cyclopentenones come from hemicellulose [63]. In the stage >25 min, the major component was phenolic substances and their derivatives produced by lignin pyrolysis. At the stage of 5-25 min, the pyrolysis products of the sample were the highest, indicating that the ketone content was high [64]. According to the properties of compounds at different stages, most of the compounds identified were organic acids, ketones, furans, cyclopentenes, phenols and their derivatives [65]. Most of these compounds are used in biopharmaceutical, chemical and energy industries [66,67].  Many of the pyrolysis products identified by Py/GC-MS detection can be used in the chemical industry as green energy. For example, acetaldehyde belongs to biomass-derived oxygenated compounds, which are one of the main components of bio-oil. Acetaldehyde is mainly used as a reducing agent and is industrially used in the manufacturing of polyacetaldehyde, acetic acid, synthetic rubber, etc. [68]. Formic acid is a major product of carbohydrates derived from biomass and is receiving increasing attention as a sustainable hydrogen source. Formic acid-mediated biomass feedstock can be converted into value-added products, including biofuels, levulinic acid, etc. [69]. Catechol is an industrially relevant chemical with countless applications. It is the most representative basic structure unit in lignin, and it is also the main reaction intermediate and product in biomass or lignin pyrolysis [70]. Catechol plays an important role in many systems by interacting with organic and inorganic compounds. In addition, catechol crosslinked polymer networks exhibit remarkable mechanical strength, good adhesion and realistic properties [71].
Biomass provides an important source of raw materials, and is ideal for the development of functional or intermediate molecules for chemical synthesis, such as glycerol carbonate or glycidol [72]. Maltol is one of the derivatives of biomass, and maltol by-products have a certain synergistic effect with pine chips. Adding less than 10% maltol by-products to pine wood chips to make a fuel blend can improve combustion characteristics and reduce emissions [73]. 1,2-cyclopentanedione, 3-methyl-is an orthocyclodione, which is an important fine chemical intermediate and is widely used in pharmaceutical, chemical and other industries [74]. Phenol, 2-methyl-can be used in organic synthesis and also as a disinfectant and preservative; it is an important pharmaceutical intermediate. It is also the main compound in bio-oils [75]. Creosol is a lignin derivative of biomass and is a high value-added product, as a source of renewable assets of great interest to industry [76,77]. Similarly, the thermal cracking products detected by Py/GC-MS also contain chemical components such as furfural [50][51][52], dihydroxyacetone [53,54], and 5-hydroxymethylfurfural [55,56]. Analysis of pyrolysis products shows that the chemical components in S. holocarpa wood can be well applied in chemical, bioenergy and other fields. At the same time, the test results of Py/GC-MS and GC-MS were also consistent, which further demonstrates the potential of S. holocarpa wood for use as a source for bioenergy production.

1 H-NMR Analysis
The 1 H-NMR spectrum of the nuclear magnetic resonance spectrum is the most widely used. It not only offers high magnetic detection sensitivity, but the signal is easy Many of the pyrolysis products identified by Py/GC-MS detection can be used in the chemical industry as green energy. For example, acetaldehyde belongs to biomass-derived oxygenated compounds, which are one of the main components of bio-oil. Acetaldehyde is mainly used as a reducing agent and is industrially used in the manufacturing of polyacetaldehyde, acetic acid, synthetic rubber, etc. [68]. Formic acid is a major product of carbohydrates derived from biomass and is receiving increasing attention as a sustainable hydrogen source. Formic acid-mediated biomass feedstock can be converted into valueadded products, including biofuels, levulinic acid, etc. [69]. Catechol is an industrially relevant chemical with countless applications. It is the most representative basic structure unit in lignin, and it is also the main reaction intermediate and product in biomass or lignin pyrolysis [70]. Catechol plays an important role in many systems by interacting with organic and inorganic compounds. In addition, catechol crosslinked polymer networks exhibit remarkable mechanical strength, good adhesion and realistic properties [71].
Biomass provides an important source of raw materials, and is ideal for the development of functional or intermediate molecules for chemical synthesis, such as glycerol carbonate or glycidol [72]. Maltol is one of the derivatives of biomass, and maltol byproducts have a certain synergistic effect with pine chips. Adding less than 10% maltol by-products to pine wood chips to make a fuel blend can improve combustion characteristics and reduce emissions [73]. 1,2-cyclopentanedione, 3-methyl-is an orthocyclodione, which is an important fine chemical intermediate and is widely used in pharmaceutical, chemical and other industries [74]. Phenol, 2-methyl-can be used in organic synthesis and also as a disinfectant and preservative; it is an important pharmaceutical intermediate. It is also the main compound in bio-oils [75]. Creosol is a lignin derivative of biomass and is a high value-added product, as a source of renewable assets of great interest to industry [76,77]. Similarly, the thermal cracking products detected by Py/GC-MS also contain chemical components such as furfural [50][51][52], dihydroxyacetone [53,54], and 5hydroxymethylfurfural [55,56]. Analysis of pyrolysis products shows that the chemical components in S. holocarpa wood can be well applied in chemical, bioenergy and other fields. At the same time, the test results of Py/GC-MS and GC-MS were also consistent, which further demonstrates the potential of S. holocarpa wood for use as a source for bioenergy production.

1 H-NMR Analysis
The 1 H-NMR spectrum of the nuclear magnetic resonance spectrum is the most widely used. It not only offers high magnetic detection sensitivity, but the signal is easy to observe; organic compounds provide a large number of hydrogen atoms in a variety of Molecules 2023, 28, 299 8 of 17 chemical environments. As can be seen from Figure 6, the overall displacement ranges from 0-8 ppm. Typically, the chemical shifts of the protons were saturated at δ 0.2 to δ 1.5 alkane compounds; usually, the first proton appears at about δ 0.9, the second proton appears at δ 1.3, and the third proton appears at δ 1.5 [78]. Generally, the proton chemical shift of the carbon atom directly connected to the halogen between 2.0 and 4.5, and the influence of the proton on the adjacent carbon atom was significantly decreased. The chemical shift of α-C protons near carbonyl or cyano was 2-3 ppm, which was caused by the anisotropic effect of C=C and sp 2 hybridization of internal changes in olefin carbon. The chemical shift in the range of 4.5-5.9 ppm belongs to olefin compounds, and the δ value increases after coupling with the aryl group [79]. Chemical shifts of 1.7-3.5 ppm were alkyne carbon protons. The chemical shifts of the carbonyl α-H belong to carbonyl compounds between 2 and 2.7 ppm, and the chemical shifts of the acid compounds range between 2 and 2.6 ppm. Displacement in the 3.3-4 ppm range is mainly caused by α-H hydrogen atoms in the ether molecule. The chemical shift of the α-H hydrogen atom in the alcohol molecule was 3.4-4 ppm, and the displacement of ester compounds and phenolic hydroxyl protons was 2-4.1 ppm and 4-8 ppm, respectively. The aromatic compound chemical shifts range from 6.3 to 8.5 ppm, and the heterocyclic aromatic protons range from 6.0 to 9.0 ppm [80].
Molecules 2023, 28, x FOR PEER REVIEW 8 of 17 chemical environments.. As can be seen from Figure 6, the overall displacement ranges from 0-8 ppm. Typically, the chemical shifts of the protons were saturated at δ 0.2 to δ 1.5 alkane compounds; usually, the first proton appears at about δ 0.9, the second proton appears at δ 1.3, and the third proton appears at δ 1.5 [78]. Generally, the proton chemical shift of the carbon atom directly connected to the halogen between 2.0 and 4.5, and the influence of the proton on the adjacent carbon atom was significantly decreased. The chemical shift of α-C protons near carbonyl or cyano was 2-3 ppm, which was caused by the anisotropic effect of C=C and sp 2 hybridization of internal changes in olefin carbon. The chemical shift in the range of 4.5-5.9 ppm belongs to olefin compounds, and the δ value increases after coupling with the aryl group [79]. Chemical shifts of 1.7-3.5 ppm were alkyne carbon protons. The chemical shifts of the carbonyl α-H belong to carbonyl compounds between 2 and 2.7 ppm, and the chemical shifts of the acid compounds range between 2 and 2.6 ppm. Displacement in the 3.3-4 ppm range is mainly caused by α-H hydrogen atoms in the ether molecule. The chemical shift of the α-H hydrogen atom in the alcohol molecule was 3.4-4 ppm, and the displacement of ester compounds and phenolic hydroxyl protons was 2-4.1 ppm and 4-8 ppm, respectively. The aromatic compound chemical shifts range from 6.3 to 8.5 ppm, and the heterocyclic aromatic protons range from 6.0 to 9.0 ppm [80]. The results of 1 H-NMR detection showed that S. holocarpa wood was rich in chemical components, including acids, ethers, alcohols, esters, aromatics and other organic compounds. Bio-oil is a complex mixture of highly oxygenated organic components, including almost all types of oxygenated organic compounds. S. holocarpa wood has the potential to become a green and sustainable energy source. This was consistent with FT-IR, GC-MS, TGA and Py/GC-MS test results.

13 C-NMR Analysis
Organic elements are the skeleton of carbon, currently 13 C-NMR spectroscopy is used to study the structure of sample changes through carbon atoms to understand the structure of organic compounds. Since some of the functional groups in the organic compound do not contain hydrogen atoms, these functional groups cannot be obtained from the 1 H spectrum and can only be obtained from the 13 C spectrum (Figure 7). For carbohydrates, the polymer carbon is mainly distributed in the 50-110 ppm region [81]. The carbon spectrum of saturated hydrocarbons, partial alkynes and partial olefins were mainly distributed between 15-45 ppm and 75-55 ppm. The carbon spectrum containing halogen elements (C-I: 0-40 ppm; c-bromine: 25-65 ppm; C-ci: 35-80 ppm) and the carbon spectrum of aromatic and olefins (=C-: 100-150 ppm; C6H6: 110-160 ppm) were mainly distributed The results of 1 H-NMR detection showed that S. holocarpa wood was rich in chemical components, including acids, ethers, alcohols, esters, aromatics and other organic compounds. Bio-oil is a complex mixture of highly oxygenated organic components, including almost all types of oxygenated organic compounds. S. holocarpa wood has the potential to become a green and sustainable energy source. This was consistent with FT-IR, GC-MS, TGA and Py/GC-MS test results.

13 C-NMR Analysis
Organic elements are the skeleton of carbon, currently 13 C-NMR spectroscopy is used to study the structure of sample changes through carbon atoms to understand the structure of organic compounds. Since some of the functional groups in the organic compound do not contain hydrogen atoms, these functional groups cannot be obtained from the 1 H spectrum and can only be obtained from the 13 C spectrum (Figure 7). For carbohydrates, the polymer carbon is mainly distributed in the 50-110 ppm region [81]. The carbon spectrum of saturated hydrocarbons, partial alkynes and partial olefins were mainly distributed between 0-80 ppm and 10-160 ppm. The signals at 20.3 ppm and 172.9 ppm shifts were mainly assigned to hemicellulose acetyl [82][83][84].

Sources of Sample and Extractives
S. holocarpa wood was collected from Xiaoqinling National Forest Park, Henan Province, and the wood sample was obtained from the trunk. The sample was processed into two different particle sizes, which were 40-60 µm and 200 µm powder. The powder with particle size of 40-60 µm was prepared for extraction, while the 200 µm powder was prepared for pyrolysis. About 15 g of the 40-60 µm powder was weighted, and extraction was performed in different organic solvents. Four types of organic solvent were prepared with optimum extraction temperature, including ethanol (75 • C), methanol (65 • C), benzene/ethanol (1:1) (90 • C) and ethanol/methanol (1:1) (70 • C). The extraction was performed for 5 h. After extraction, the four extracts were separated, and the excess solvent was removed with a rotary evaporator. The concentrated extracts were now ready for FT-IR and GC-MS analysis.

FT-IR Analysis
About 1 mL of extractives and 1 g KBr were mixed and pressed into KBr tablets which were, respectively, detected using a Thermo Fisher Nicolet iS10 FT-IR spectrophotometer (Waltham, MA, USA) by KBr method [90].

GC-MS Analysis
Each of the four extracts was tested on the Agilent-7890B-5977A (Santa Clara, CA, USA) instrument. Elastic quartz capillary columns (HP-5MS: 30 m × 250 µm × 0.25 µm) were used. The carrier gas flow rate was 1 mL/min; the carrier gas used was high purity helium, and the split ratio was set at 2:1. First, the temperature rises gradually from 50 • C to 250 • C at a rate of 8 • C/min, and then from 250 • C to 300 • C at a rate of 5 • C/min. The program was set to scan quality ranges, ionization voltages, ionization currents, ion sources and four-pole data for 30-600 amu, 70 eV, 150 ua, 230 • C and 150 • C [91].

TGA Analysis
Analysis of the 1 mg 200 µm powder was performed on a Perkin Elmer-STA8000 (Waltham, MA, USA) instrument. The temperature was set to rise from 30 • C-300 • C at the rate of 5 • C/min. The carrier gas rate was set at 60 mL/min and the gas used was nitrogen [92].

Py/GC-MS Analysis
About 0.1 mg of the powder sample (200 mu) was placed in an Agilent-7890B-5977A CDS5000 (Santa Clara, CA, USA) instrument for analysis and detection. The carrier gas, pyrolysis temperature, heating rate and pyrolysis time used were helium (high purity), 500 • C, 20 • C/ms and 15 s, respectively. The capillary column (HP-5MS: 60 m × 250 µm × 0.25 µm), pyrolysis product delivery line, injection valve temperature, shunt ratio and shunt velocity were 300 • C, 300 • C, 1:60 and 50 mL/min, respectively. The GC was programmed to last for 2 min at 40 • C, increasing from 40 • C to 120 • C at a rate of 5 • C/min. At 10 • C/min, it went from 120 • C to 200 • C for 15 min. The MS ion source temperature and scanning range was 230 • C and 28-500 amu. [93].

NMR Analysis
The NMR polarizer model is Agilent-400 MR (Santa Clara, CA, USA) and methanol-d4 was the solvent used in the testing process. The entire assay was performed with the same NMR probe: 1 H-NMR, 13 C-NMR, and 2D-NMR. The duration, sample-and-hold time, pulse, pulse width and frequency of 1 H-NMR were 1.000 s, 2.556 s, 45 degrees, 6410.3 Hz and 399.79 MHz, respectively. The duration, sample-and-hold time, pulse, pulse width, frequency, hydrogen decoupling frequency and power of 13

Conclusions
This project utilized S. holocarpa wood as the research object to evaluate its potential as a lignocellulosic biomass source for bioenergy production The results proved that S. holocarpa wood contains a large amount of organic chemicals that can be used in the bioenergy and chemical industries. This project also provides the research basis of S. holocarpa wood pyrolysis, in which a large number of volatile compounds (including ketones, alcohols and phenol) were detected, which are proven to be important organic components of bio-oil. The NMR detection method used to identify the distribution of functional groups also proved that S. holocarpa wood has the potential to become a biomass energy source. This study explores the relationship between potential of the extraction and the pyrolysis of S. holocarpa wood, which is helpful for the exploitation and utilization of S. holocarpa wood as for bioenergy production. For the first time, NMR technology has been applied to S. holocarpa wood, and pyrolysis products show the potential to become high-value products. In the future, pyrolysis with various parameters can be optimized to maximize bioenergy production.
Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/molecules28010299/s1, Table S1: GC-MS analysis of ethanol sample; Table S2: GC-MS analysis of the methanol sample; Table S3: GC-MS analysis of benzene/ethanol sample; Table S4: GC-MS analysis of the ethanol/methanol sample; Table S5: Py/GC-MS analysis of S. holocarpa wood.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author.

Conflicts of Interest:
The authors declare no conflict of interest.