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Article

Production of Syngas and Hydrogen-Rich Gas from Lignocellulosic Biomass via Ru/Al2O3 Catalyst-Assisted Slow Pyrolysis

by
Pavel Straka
*,
Jaroslav Cihlář
and
Olga Bičáková
Institute of Rock Structure and Mechanics, v.v.i., Czech Academy of Sciences, V Holešovičkách 94/41, 18209 Prague, Czech Republic
*
Author to whom correspondence should be addressed.
Catalysts 2025, 15(11), 1033; https://doi.org/10.3390/catal15111033 (registering DOI)
Submission received: 30 September 2025 / Revised: 23 October 2025 / Accepted: 30 October 2025 / Published: 1 November 2025
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Abstract

The aim of this work is to present a technologically feasible method for processing biomass into synthesis gas or hydrogen-rich gas. Three types of biomass with different lignin contents were pyrolyzed in a pyrolysis unit under well-defined conditions (ambient pressure, heating rate of 10 K min−1, end temperature of 500 °C, operating particle size, variable catalyst mass) in the presence of a ruthenium catalyst (Ru/Al2O3, powder), and the effect of catalyst amount on the yield and gas composition was observed. Feedstock mass was always 50 g, and catalyst mass was 2.5, 5, and 10 g (mixing ratios 0.05, 0.1, and 0.2, resp.). During pyrolysis, the raw gas and vapors was passed through the catalyst bed and converted to the resulting gas and bio-oil. The gas obtained was cleaned by sequestration with CO2 using commercial active carbon to obtain syngas with different H2/CO ratios or hydrogen-rich gas. It was found that, depending on the catalyst amount, slow pyrolysis catalyzed by ruthenium yielded syngas with a H2/CO ratio of approximately 0.5–5, which is further usable. The by-products obtained (bio-oil and biochar) are also described. Bio-oils from all three biomass types contained mainly carboxylic acids (33–46 wt.%) and phenols (18–33 wt.%), hydroquinone (up to 5 wt.%), and a high amount of stearate (up to 26 wt.%). All of these compounds have high utility value. The resulting biochar can probably be applied, after activation using CO2, as a sorbent. In conclusion, under energy-efficient conditions (end temperature max. 500 °C), Ru/Al2O3-catalyzed pyrolysis of biomass provides syngas or hydrogen-rich gas and usable by-products. It should be emphasized that the maximum theoretical H2 production from biomass is 60–70 g H2/kg biomass. This limit value could negatively affect the technological development of the process.

1. Introduction

Biomass is one of the largest sources of renewable energy available. The advantage of biomass waste is its low cost and good availability in sufficient quantities [1], especially for processing into energy (to illustrate, prices for wood residues can be 15–30 and 64–77 USD/ton in USA and Europe, respectively; for agricultural residues 20–50 and 55–68 USD/ton in USA and Europe, resp. (IRENA, Biomass, Cost Analysis Series, 2012–2024)). Efficient production of syngas—a gaseous mixture of hydrogen and carbon monoxide—from the pyrolysis of agricultural biomass largely depends on the optimization of operational parameters and the selection of suitable catalysts. High reaction temperatures are known to promote thermal cracking of biomass and the subsequent conversion of volatile compounds into syngas [1]. These processes also serve to minimize the formation of liquid by-products such as bio-oil and tar [2]. Moreover, catalysts have been shown to play a crucial role in enhancing syngas yield and adjusting the H2/CO ratio. Catalysts also prevent their own deactivation by reducing tar and coke formation [3]. Nickel-based catalysts are particularly favored due to their high activity and relatively low cost compared to noble metals. They demonstrate strong performance in the reforming of pyrolysis vapors [4,5,6,7,8]. Natural minerals such as dolomite (CaMg(CO3)2) [9] and olivine ((Mg,Fe)2[SiO4]) [10] have been shown to support in situ tar reforming and the water–gas shift reaction. Their nickel-modified variants (e.g., Ni–Ce olivine) have also proven effective in promoting tar cracking and increasing syngas output [11]. The integration of these catalysts under optimized conditions—such as controlled heating rates and gas-residence times—facilitates a more selective and economically viable conversion of agricultural waste into high-quality syngas, offering a sustainable pathway for biofuel production [12]. It should be emphasized that the catalysts mentioned are effective at higher temperatures, such as 800–900 °C.
Concerning studies focused on the use of rhodium-based catalysts in syngas production via pyrolysis, the work by Ammendola et al. [13] is particularly noteworthy. The study reports that the application of rhodium in combination with perovskite supported on alumina significantly increased the syngas yield during maple sawdust pyrolysis.
Also effective is the Rh/CeO2/SiO2 catalytic system employed in the study by Tomishige et al. [14], which exhibited a higher syngas yield than conventional Nickel-based catalysts. This catalytic system is productive at temperatures of 600–700 °C. The experiments focused on the application of this catalyst in cedar wood gasification using a small amount of either oxygen or steam.
The use of coal-derived bottom tar as a catalyst in the pyrolysis of rice husks was found to increase syngas production in comparison with non-catalytic pyrolysis. The results confirmed the hypothesis that industrial waste tar—a low-cost material—could be employed for assisted catalysis. The catalytic activity is attributed to trace amounts of metals present in the tar [15].
Nickel-based catalysts are widely used in various research and industrial applications due to their versatility and relatively low cost compared to precious metals. In a study on poplar wood pyrolysis, Zsinka et al. [16] found that the presence of Ni/Al2O3 increased syngas yield by as much as threefold. Moreover, the catalyst regained its activity after CO2 regeneration, and its syngas selectivity was further enhanced. The study also included tests of other nickel-modified catalysts, such as dolomite and zeolite. Ni/dolomite was found to suppress tar formation and reduce CO2 content in the resulting gas, while nickel promoted an increase in H2 and CO concentrations. A representative natural zeolite, Ni/clinoptilolite, demonstrated CO2 capture capability, thereby improving the purity of the produced syngas.
Two-stage catalytic pyrolysis using nano-NiO/Al2O3 was investigated by Xu et al. [17]. Pine sawdust was selected as the feedstock, and the catalyst was found to eliminate tar formation effectively. The highest syngas yield was achieved by extending the pyrolysis duration, with residence times up to 30 s. The optimal temperature was identified as 800 °C, resulting in a gas yield of 93%. Similarly, Yang et al. [18] conducted two-stage catalytic pyrolysis of corn stalks. The resulting volatiles were cracked using a bifunctional Fe/CaO catalyst, producing hydrogen-enriched syngas.
To convert apricot stone shells into syngas via pyrolysis, it is essential to control the heating process so that the temperature remains within the desired range, typically between 600 and 900 °C [19,20]. Elevated temperatures are crucial for the breakdown of the lignocellulosic structure, which facilitates the secondary reforming of volatile compounds into the target syngas mixture of H2 and CO [19,21]. The use of a catalyst is particularly advantageous for in situ tar cracking and syngas composition improvement. The catalyst investigated for the pyrolysis of apricot pit kernels was MCM-41 doped with aluminum, cobalt or iron. Although it influenced the composition of the resulting syngas, it had little effect on increasing overall gas yield [22].
Walnut shells, which are rich in carbon, represent another promising feedstock for syngas production. Optimal conditions for their pyrolysis also involve elevated temperatures (up to 750 °C), with maximum gas yields observed at approximately 950 °C [23]. The addition of ZnCl2 and alkali metal-based catalysts (K2CO3, Na2CO3) significantly improved syngas quality and increased hydrogen content [24,25]. In a separate study, carbonate-based catalysts were applied to biomass pyrolysis, with K2CO3 yielding the most favorable results [8]. The role of carbonates is to facilitate secondary tar cracking, which leads to higher gas yields and a more favorable H2/CO ratio. Another research group developed a Ni/olivine/La2O2/ZrO2 catalytic system, which produced the highest gas output at 1100 °C via a tar-reforming mechanism [26].
Birch sawdust pyrolysis has been investigated with the aim of increasing the yield of volatile compounds. For this purpose, a bubbling fluidized bed reactor was employed. It was found that fast pyrolysis in a fluidized bed produced substantial amounts of bio-oil, along with syngas and biochar [27]. Product distribution is strongly influenced by temperature; elevated temperatures facilitate the decomposition of complex organic compounds into gaseous species such as hydrogen and carbon monoxide.
Catalyst application has also been studied to improve pyrolysis product yields and influence their composition [28]. The use of zeolite-based catalysts was shown to increase the overall yield of gaseous and liquid products while significantly altering their chemical profile. This led to higher concentrations of compounds such as phenols, furans, and hydrocarbons. Overall, it appears that the catalysts studied so far are effective at temperatures of 600–900 °C, but also at 1100 °C, as mentioned above.
This work focuses on the catalytic pyrolysis of birch sawdust, apricot stones, and walnut shells at the end temperature of 500 °C. It seems that catalyzed thermochemical conversion of biomass into syngas is a promising area of research. However, it is essential to optimize operational parameters to ensure acceptable syngas yield and composition as well as the usability of by-products. In our study, we examined the effect of a Ru-based catalyst supported on Al2O3. To date, biochar has been used as a ruthenium carrier for syngas methanation [29].

2. Results and Discussion

2.1. Mass Balance of the Process

First, the mass balance of the process was determined. (For initial biomass, see Table 1 and Table 2 in Section 2). The results are summarized in Figure 1, which shows that, quantitatively, the main products are bio-oil and biochar. Bio-oils obtained were somewhat moist, which is common for pyrolysis oils. Therefore, this item is marked as the liquid fraction in Figure 1. The yield of total pyrolysis gas was 12–17 wt.%. Since the losses were acceptable, 3–9 wt.%, the mass balance achieved can be used for further considerations. The catalyst appears to promote gas formation to a certain extent, as its addition of 2.5 and 5 g increased the amount of gas from 11.7 to 14.4 wt.% in the case of BS, from 13.6 to 17.2 wt.% in the case of WS, and from 14.7 to 16.8 wt.% in the case of WS. Conversely, in all the cases, a lower yield of bio-oil obtained with the catalyst was recorded compared to the yield without it. The mass balance given is only preliminary because the gas obtained was cleaned with a carbon sorbent to remove carbon dioxide. This changed its density and thus the gas to losses ratio. Gas density can play a role in applications with synthesis gas or hydrogen-rich gas; therefore, attention was paid to the physical properties of cleaned gas (see below).

2.2. Composition and H2/CO Ratio of Pyrolysis Gas

At a final temperature of 500 °C, the composition of the obtained gas—after removal of most of the CO2—was relatively favorable when using Ru/Al2O3 catalysis, both in the case of BS, AS, and WS pyrolysis, because the hydrogen and CO contents were 26–82 and 16–50 vol. %, respectively, Table 3. Note that syngas typically contains 25–30 vol.% hydrogen and 30–60 vol. % CO. Since hydrogen-rich gas is also considered, a higher H2 content (51–82 vol.%) and a relatively low content CO (16–26 vol.%) are also favorable results.
As for the other components of the gas obtained by catalysis, the methane content was low or at least acceptable (1–10 vol.%, usually it is below 5 vol.% for syngas); CO2 content was 1–15 vol.% (typically 5–15 vol.% for syngas); and no ammonia, methylamine, H2S, COS, or CS2 were found. The H2/CO ratio in the case of uncatalyzed pyrolysis was 0.34–0.64. However, such a ratio is very narrow and insufficient, because different products require very different ratios for optimal yields, for example a 2:1 for methanol. Generally, the H2/CO ratio in syngas varies considerably depending on the feedstock and process used with specific applications requiring different ratios. E.g., syngas from coal gasification often has this ratio of approximately 1:1 to 2:1, which is suitable for methanol production or Fischer–Tropsch synthesis [30]. However, syngas from biomass typically suffers from a lack of hydrogen and therefore has a low H2/CO ratio, often less than 1 [31]. Using the Ru/Al2O3 catalyst, the H2/CO ratio was achieved in a substantially larger range, 0.52–5.19 (Table 3), depending on the amount of catalyst. This means that the gas obtained in this way has a much wider range of applications. Table 3 shows that with increasing amount of catalyst, the hydrogen concentration changes the most, compared to the other components. These changes seem to be caused by the lignin concentration in the biomass, as the largest increase in hydrogen was observed in WS, which also has the highest lignin content (see Table 2, Section 2.1). The hydrogen elimination from lignin is promoted by a ruthenium catalyst (see below).
As can be further seen from Table 3, hydrogen-rich gas was obtained in the presence of catalyst in amounts of 10 and 20 wt.%, and in the case of WS also with 5 wt.% (related to the feedstock mass). The hydrogen-rich gas obtained contains 51–82 vol.% H2 and can be used for further utilization. Therefore, the utility properties of gas, namely higher heating value (HHV), lower heating value (LHV), and gas density (d), were determined (Table 4). The values given in Table 4 show that the obtained gas can be used similarly to hydrogen, since it has a comparable HHV (11.99–13.59 MJ m−3; for hydrogen it is 11.89 MJ m−3) and LHV (10.54–12.11 vs. 10.70 MJ m−3). As expected, the gas density is significantly higher compared to hydrogen (0.307–0.729, vs. 0.084 kg m−3), but from a usage perspective this is not a major problem, as can be seen from the overview of possible applications of hydrogen-rich gas from biomass [32].
The conclusion that Ru/Al2O3 promotes hydrogen production from biomass is also supported by the hydrogen evolution during pyrolysis (Figure 2, Figure 3 and Figure 4). It seems that hydrogen production is conditioned by the lignin content of the biomass, since in the case of BS (lignin content 23%; C 63, H 4, O 33 wt.%) (Figure 2) the H2 development is significantly lower than in the case of AS (31%; C 47, H 6, O 46 wt.%) (Figure 3), and WS (48%; C 48, H 7, O 44 wt.%) (Figure 4). The catalyst therefore promotes lignin cleavage, so that with increasing lignin content more H2 is produced.
The course of hydrogen evolution in the presence of the catalyst differs for BS compared to AS and WS. The evolution of H2 is therefore also influenced by other factors, in particular the heating rate. At different biomass compositions, a given heating rate of 10 K min−1 can lead to different temperatures of the onset of hydrogen cleavage (for AS and WS it was about 410 and 390 °C, respectively (Figure 3 and Figure 4), but for BS about 470 °C (Figure 2). The different temperatures of the onset of cleavage are then reflected in the different courses of the H2 evolution curves.

2.3. Composition of Bio-Oil

The mass balance of the process (Figure 1) shows that the bio-oil yields were high (40–52 wt.%). Therefore, GC-MS analysis of the bio-oils obtained from the biomass investigated in the presence of catalysts was performed. The determined composition is shown in Table 5.
Table 5 shows that catalytically obtained bio-oils from all three biomass types contained mainly carboxylic acids (33–46 wt.%) and phenols (18–33 wt.%). The amount of hydroquinone (up to 5 wt.%) is notable, as is the high amount of stearate in the case of AS (26 wt.%). All of these compounds have high utility value and extensive use in industries.
The occurrence of organic compound types in bio-oils is illustrated in Figure 5. Liquid hydrocarbons and stearates are mainly provided by catalyzed pyrolysis of AS, but naphthalenes and substituted benzaldehydes are not produced by this pyrolysis. Toluene, 2-hexanone, and cyclohexanones are mainly obtained from BS pyrolysis. The most important compounds—phenols, carboxylic acids, and hydroquinone—were provided in varying degrees by all biomasses examined.
Table 5 and Figure 5 show a particularly high stearate content in AS bio-oil compared to BS and WS. This is certainly related to the high content of extractives in AS (Table 2). It is well known that these extractives have a high concentration of fatty acids, including stearic acid. Therefore, pyrolysis released stearates in high amounts, as shown in Table 5. In this case, the amount of fatty acids in extractives was so high that stearates were formed at the expense of phenols.
A dramatic decrease in hydroquinone was observed in all three bio-oils due to the action of the catalyst. This decrease was reflected in the BS bio-oil by an increase in phenols (from 21 to 33 wt.%) and in the WS bio-oil by an increase in ketones (from 4.5 to 9.5 wt.%) (Table 5). (This cannot be assessed for AS bio-oil, because the high proportion of extractives in AS caused the dominant proportion of stearates in the bio-oil, as above). Furthermore, in all cases, the formation of acetophenone derivatives was observed due to the action of the catalyst.

2.4. Composition and Properties of Biochar

Biochar can be used in various ways (biofuel, sorbent, soil additive, catalyst carrier). In this case, its use as a biofuel was considered based on the work [33]. Therefore, all characterization parameters including the higher heating value and the lower heating value LHV were first determined for obtained biochar (Table 6).
Table 6 shows that under the above conditions a high-quality biofuel was obtained, as it has a low ash content (2–8 wt.%) and a very low sulfur content (mainly 0.05–0.07 wt.%, exceptionally 0.10 and 0.13 wt.%). At the same time, it has a high HHV and LHV, at 28–34 and 27–33 MJ kg−1 (exceptionally 24 and 23 MJ kg−1). It therefore has better energy properties than conventional hard coal, whose HHV and LHV are typically 28–30 MJ kg−1 and 27–29 MJ kg−1. Given the low ash and sulfur content, it can be concluded that the studied biomass provides a usable biofuel under the above conditions.
Another use of biochar is as a carbonaceous sorbent. It is known that up to 90% of the internal surface of carbon sorbents is covered with micropores. Therefore, their surface area (Smicro) was first determined. As expected, the addition of the catalyst had no effect on Smicro, as the catalyst affected the cleavage of the resulting volatile compounds. The results are summarized in Table 7. Given values show that for practical use it is necessary to activate the obtained biochar, e.g., with air or carbon dioxide at a higher temperature, e.g., 800 °C. It is clear that the obtained biochars have certain prerequisites for use as sorbents, but their activation requires further attention.
To illustrate the porous texture, two distinct porous textures observed in biochar obtained are pictured: reticulated and with porous walls (Figure 6 and Figure 7). It is highly likely that these two textures determine the porous nature of biochar and thus its sorption predisposition.

2.5. Possibilities of Re-Use or Regeneration of Catalyst Used

Ruthenium catalyst can be regenerated by chemical methods [34,35,36], but it seems that Ru/Al2O3 in particular can be reused. In this case, this was possible because the catalyst was located above the sample, so it is not mixed with the charge. As mentioned, during pyrolysis, the raw gas was passed through the catalyst bed. It is quite certain that the catalyst can be used 5 times. Since it is possible to ensure the placement of the catalyst in the bed above the charge even under operating conditions, catalyst reuse is likely possible on a large scale, both in batch and continuous mode.

3. Materials and Methods

3.1. Materials

Experiments were performed using birch wood shavings (BS), apricot stones (AS), and walnut shells (WS). The proximate, ultimate, and biochemical analysis of the wastes used are given in Table 1 and Table 2.
As a catalyst, ruthenium dispersed on a porous Al2O3 matrix (BET 272 m2 g−1) was used while the loading of Ru was 5 wt.% (Merck Sigma-Aldrich, s.r.o., Darmstadt, Germany, powder with moisture content < 2 wt.%) (Ru/Al2O3 catalyst, see Figure 8 and Figure 9).

3.2. Methods

The waste biomass was pyrolyzed in a laboratory pyrolysis unit (Figure 10) consisting of a vertical electric resistance furnace with programmable heating, a quartz reactor with volatile product exhaust, a flask for capturing liquid products, a cooling system for volatile products (two coolers in series cooled with ethylene glycol at a temperature −10 °C), and a gasholder with a capacity of 130 dm3. The unit was equipped with continuously operating analyzers (an infrared CH4, CO, and CO2 analyzer (Teledyne Analytical Instruments, Industry, CA, USA, model 7500) and an electrochemical hydrogen analyzer (Calomat 6, Siemens Industry, Inc., Buffalo Grove, IL, USA), continuous temperature sensing of reactor wall, a reactor interior, and released volatile products, as well as continuous sensing of the volume and pressure of the developed gas, and a cooling control. The heating was controlled by a programmable module while all sensed data were recorded by the control PC. Its design makes it possible to reduce losses in the pyrolysis of charges up to 100 g to a maximum of 5 wt.%, most commonly to 2–4 wt.%. Pyrolysis was performed both with and without catalyst. During catalyst-assisted pyrolysis, the raw gas was passed through a bed with a catalyst layer. Feedstock mass was always of 50 g, and the catalyst mass was 2.5, 5, and 10 g. The heating rate was 10 K min−1, end temperature was 500 °C, and the delay at the end temperature was 60 min. Each pyrolysis run was carried out three times. The relative standard deviation of oil yield was 1–2%, the solid carbon residue yield was 4–5%, and pyrolysis gas yield 1–2%.
Analysis of obtained gas was carried out on two Agilent (Santa Clara, CA, USA) Technologies 6890N gas chromatographs. Oxygen, nitrogen, and carbon monoxide were determined on a HP-MOLSIV capillary column (40 °C) with helium as the carrier gas (5 cm3 min−1) using TCD, while CH4 and other gas hydrocarbons were determined on a GS-Gaspro capillary column (60 °C) with N2 as the carrier gas (20 cm3 min−1) using FID (air 400 cm3 min−1, H2 30 cm3 min−1, N2 20 cm3 min−1). Carbon dioxide was determined on a GS-Gaspro capillary column (40 °C) with He as the carrier gas (5 cm3 min−1) using TCD. Hydrogen was determined on a HP-5 capillary column (40 °C) with N2 as the carrier gas (7 cm3 min−1) using TCD.
To clean the pyrolysis gas, especially to capture CO2, commercially available activated carbon (AC) (Brenntag CR, s.r.o., Prague, Czechia) was used. This granular AC (size ~4 mm) had a specific surface area (BET) of approximately 1000 m2/g.
The components of bio-oils were determined using GC-MS on an Agilent Technologies 6890 chromatograph with MSD 5973 mass spectrometer. A capillary column (30 m × 0.25 mm) DB XLB was used. He served as the carrier gas. For the first minute, the column was maintained at the temperature of 50 °C. The temperature was then increased to 280 °C or 300 °C with a gradient of 10 K min−1. The delay at 280 °C/300 °C lasted six min.
The biochar obtained was analyzed according to EN ISO standards: EN ISO 16948 [37], EN ISO 16994 [38], EN ISO 18122 [39], and EN ISO 18134 [40]. The surface area of the micropores of the biochar obtained was determined by gravimetric sorption analysis. CO2 isotherms were measured on a Hiden IGA 002 gravimetric sorption analyzer. In the course of the sorption process, the sample temperature was automatically controlled within the range of ±0.05 °C, and the pressure converter worked with an accuracy ±0.02%. The long-term stability of the microbalance was ±1 μg with a weighing resolution of 0.2 μg. The time approaching the equilibrium state was analyzed and the weight change was recorded upon reaching 98% of an asymptotic value, according to a computer algorithm. For CO2 sorption, samples were prepared with grain size < 0.2 mm and sample weight was chosen with respect to the high sensitivity of the balance and expected sorption capacity, about 0.3 g. Before measurement, the samples were degassed at a temperature of 373 K under vacuum 10−6 Pa for 6 h minimally up to zero weight decrease. The measurements were performed at a temperature of 298 K over a low relative pressure range up to 0.015.

4. Conclusions

Under energy saving conditions (end temperature max. 500 °C, ambient pressure), slow Ru/Al2O3-catalyzed pyrolysis of biomass provides syngas or hydrogen-rich gas and exploitable by-products. Depending on the amount of catalyst, this pyrolysis yielded synthesis gas with a wide range of H2/CO ratios of 0.5–5, which is further applicable. The obtained by-products, bio-oil and biochar, are or may be useful. Bio-oils from the three biomass types mainly contained carboxylic acids (33–46 wt.%) and phenols (18–33 wt.%), hydroquinone (up to 5 wt.%), as well as a high amount of stearate (up to 26 wt.%). All of these compounds have a high utility value. The biochar obtained has potential as a sorbent, but only after activation, preferably with CO2.

Author Contributions

P.S.: Investigation, Methodology, Writing—original draft, Writing—review & editing. O.B.: Methodology, Formal analysis. J.C.: Methodology, Formal analysis. All authors have read and agreed to the published version of the manuscript.

Funding

This work was carried out thanks to the support of the Long-Term Project for the Conceptual Development of the Research Organization No. RVO 67985891, and the Strategy AV21 Research Program of the Czech Academy of Sciences: Sustainable Energy (VP27).

Data Availability Statement

Data is contained within the article.

Conflicts of Interest

The authors declare no conflict of interest.

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Catalysts 15 01033 g001
Figure 1. Mass balance (wt.%) of slow pyrolysis of birch shavings (BS), apricot stone (AS), and walnut shells (WS) alone and with 2.5, 5, and 10 g Ru/Al2O3.
Figure 1. Mass balance (wt.%) of slow pyrolysis of birch shavings (BS), apricot stone (AS), and walnut shells (WS) alone and with 2.5, 5, and 10 g Ru/Al2O3.
Catalysts 15 01033 g001
Catalysts 15 01033 g002
Figure 2. Evolution of hydrogen during slow pyrolysis of BS. Blue line—without catalyst, red line—with catalyst.
Figure 2. Evolution of hydrogen during slow pyrolysis of BS. Blue line—without catalyst, red line—with catalyst.
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Catalysts 15 01033 g003
Figure 3. Evolution of hydrogen during slow pyrolysis of AS. Blue line—without catalyst, red line—with catalyst.
Figure 3. Evolution of hydrogen during slow pyrolysis of AS. Blue line—without catalyst, red line—with catalyst.
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Catalysts 15 01033 g004
Figure 4. Evolution of hydrogen during slow pyrolysis of WS. Blue line—without catalyst, red line—with catalyst. (Note: the elemental composition of BS cellulose is C 44, H 6, O 49 wt.%; that for AS is practically the same; that for WS is C: 70, H: traces, O: 30. It means that the H2 from WS must be generated from lignin. In BS and AS, the amounts of hydrogen are practically the same, so the difference in H2 development must be due to lignin).
Figure 4. Evolution of hydrogen during slow pyrolysis of WS. Blue line—without catalyst, red line—with catalyst. (Note: the elemental composition of BS cellulose is C 44, H 6, O 49 wt.%; that for AS is practically the same; that for WS is C: 70, H: traces, O: 30. It means that the H2 from WS must be generated from lignin. In BS and AS, the amounts of hydrogen are practically the same, so the difference in H2 development must be due to lignin).
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Catalysts 15 01033 g005
Figure 5. Occurrence of compounds in bio-oils obtained with 5 g Ru/Al2O3 catalyst (loading of Ru is 5 wt.%) from birch wood shavings (BS 5), apricot stones (AS 5), and walnut shells (WS 5).
Figure 5. Occurrence of compounds in bio-oils obtained with 5 g Ru/Al2O3 catalyst (loading of Ru is 5 wt.%) from birch wood shavings (BS 5), apricot stones (AS 5), and walnut shells (WS 5).
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Catalysts 15 01033 g006
Figure 6. Biochar from BS: A network-like structure copying the cellular structure, but with pores (dark).
Figure 6. Biochar from BS: A network-like structure copying the cellular structure, but with pores (dark).
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Catalysts 15 01033 g007
Figure 7. Biochar from AS: A network-like structure with pores (dark) and porous walls.
Figure 7. Biochar from AS: A network-like structure with pores (dark) and porous walls.
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Catalysts 15 01033 g008
Figure 8. Concentrations of elements of the catalyst used as found by Energy-dispersive X-ray spectroscopy (K lines, wt.%). O 40.22; Al 51.82; P 0.22; Ru 5.42; Na 0.60; Cu 0.34.
Figure 8. Concentrations of elements of the catalyst used as found by Energy-dispersive X-ray spectroscopy (K lines, wt.%). O 40.22; Al 51.82; P 0.22; Ru 5.42; Na 0.60; Cu 0.34.
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Catalysts 15 01033 g009
Figure 9. Morphology of Ru/Al2O3 catalyst used.
Figure 9. Morphology of Ru/Al2O3 catalyst used.
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Catalysts 15 01033 g010
Figure 10. A scheme of the experimental rig: 1—vertical electric resistance furnace; 2—biomass sample; 3—glass wool; 4—quartz reactor with volatile product exhaust; 5—programmable heating; 6—computer; 7—catalyst layer; 8—cooling system with separation of liquid fraction and gas; 9—two continuous analyzers and gasholder (Gas).
Figure 10. A scheme of the experimental rig: 1—vertical electric resistance furnace; 2—biomass sample; 3—glass wool; 4—quartz reactor with volatile product exhaust; 5—programmable heating; 6—computer; 7—catalyst layer; 8—cooling system with separation of liquid fraction and gas; 9—two continuous analyzers and gasholder (Gas).
Catalysts 15 01033 g010
Table 1. Proximate analysis and organic elemental analysis of birch wood shavings (BS), apricot stones (AS) and walnut shells (WS) used (as received, wt.%). VM—volatile matter, FC—fixed carbon.
Table 1. Proximate analysis and organic elemental analysis of birch wood shavings (BS), apricot stones (AS) and walnut shells (WS) used (as received, wt.%). VM—volatile matter, FC—fixed carbon.
WaterAshVMFCHCSorgNO
BS6.514.3272.8216.355.6546.640.040.5536.29
AS4.872.3081.5311.307.7856.080.176.6322.17
WS7.862.6071.5318.025.8848.500.051.3033.81
Table 2. Biochemical analysis of birch wood shavings (BS), apricot stones (AS), and walnut shells (WS) used (dry, wt.%).
Table 2. Biochemical analysis of birch wood shavings (BS), apricot stones (AS), and walnut shells (WS) used (dry, wt.%).
LigninCelluloseHemicelluloseExtractives
BS23.0144.5827.272.54
AS31.3325.3729.4511.44
WS48.0725.7122.072.33
Table 3. Gas composition (vol.%) from birch wood shavings (BS), apricot stones (AS), and walnut shells (WS) after sorption on carbonaceous sorbent, and resulting H2/CO ratio. Contents of C3H8, ∑C4 and ∑C5 were always 0.00 vol.%.
Table 3. Gas composition (vol.%) from birch wood shavings (BS), apricot stones (AS), and walnut shells (WS) after sorption on carbonaceous sorbent, and resulting H2/CO ratio. Contents of C3H8, ∑C4 and ∑C5 were always 0.00 vol.%.
Ru/Al2O3 (g)CH4C2H4C2H6C3H6N2COCO2H2H2/CO
BS015.020.060.130.000.1343.2213.9027.540.64
2.58.740.010.020.010.8841.506.4642.390.97
58.210.040.060.000.9325.2214.3451.202.03
106.020.060.130.000.3425.7915.6552.012.02
AS019.710.000.020.020.8748.121.4829.780.51
2.510.010.020.020.000.8350.0712.8726.180.52
59.890.030.070.000.9019.8813.8755.362.78
106.610.010.040.000.9318.2112.8961.313.37
WS017.180.030.040.000.6648.3017.2116.580.34
2.50.970.000.000.000.6215.821.0482.175.19
53.160.040.070.000.7116.8812.4266.733.95
101.040.000.000.000.7623.914.3569.942.93
Table 4. Physical properties of cleaned gas from catalyzed pyrolysis of birch wood shavings (BS), apricot stones (AS), and walnut shells (WS). HHV—the higher heating value, LHV—the lower heating value, d—gas density.
Table 4. Physical properties of cleaned gas from catalyzed pyrolysis of birch wood shavings (BS), apricot stones (AS), and walnut shells (WS). HHV—the higher heating value, LHV—the lower heating value, d—gas density.
BiomassRu/Al2O3 (g/wt.%)H2
(vol.%)		HHV
(MJ m−3)		LHV
(MJ m−3)		d
(kg m−3)
BS5 g/10%51.2013.0611.730.717
10 g/20%52.0112.4311.160.729
AS5 g/10%55.3613.5912.110.656
10 g/20%61.3112.8011.330.597
WS2.5 g/5%82.1712.8811.220.307
5 g/10%66.7311.9910.540.549
10 g/20%69.9412.3710.950.465
Table 5. Bio-oil composition (wt.%) from BS, AS and WS. 5 g Ru/Al2O3 was used. For comparison, the values obtained without catalyst are given.
Table 5. Bio-oil composition (wt.%) from BS, AS and WS. 5 g Ru/Al2O3 was used. For comparison, the values obtained without catalyst are given.
CompoundsBSASWSNote
withWithoutwithWithoutwithWithout
Liquid hydrocarbons
C6–C17		0.240.211.751.600.091.10Including cyclohexanes 0.14 wt.% at BS; no cyclohexanes were detected at AS and WS.
Alkylbenzenes2.402.420.350.350.690.67
Naphthalenes0.150.080.000.220.100.09
Phenols32.5720.6617.5026.1932.6233.73
Hydroquinone5.1323.622.6916.074.0117.47
Carboxylic acids33.4237.0446.1646.6241.9236.45Including esters of lower acids in a significant minority.
Benzoates2.740.001.370.000.850.00
Stearates4.880.0026.380.003.250.00
Ketones14.2512.252.883.469.524.54Cyclopentanones,
cyclohexanones, 2-hexanone.
Acetophenone derivatives1.540.000.920.002.280.00
Subst. benzaldehydes2.683.720.005.494.675.95
Sum100.00100.00100.00100.00100.00100.00
Table 6. Water, ash, and organic elemental analysis (wt.%), higher heating value (HHV, MJ kg−1), and lower heating value (LHV, MJ kg−1) of biochar obtained.
Table 6. Water, ash, and organic elemental analysis (wt.%), higher heating value (HHV, MJ kg−1), and lower heating value (LHV, MJ kg−1) of biochar obtained.
Initial
Biomass		Catalyst Amount (g)WaterAshCHNSorgOHHVLHV
BS02.093.8583.552.281.050.077.1123.9023.35
2.52.042.2186.593.010.330.055.7733.7833.07
52.414.1884.412.930.250.075.7532.2731.57
103.555.6583.202.950.140.104.4131.7130.98
AS03.482.9081.342.970.780.138.4031.4630.73
2.51.752.3285.303.020.910.056.6533.0132.31
51.375.2483.412.970.690.056.2732.2531.57
101.595.3284.732.920.840.054.5532.2731.59
WS03.142.3487.502.890.570.063.5033.2932.58
2.52.153.8784.973.050.080.055.8332.4131.69
51.657.7482.772.610.070.055.1127.8627.25
102.678.4680.102.800.170.055.7530.6129.93
Table 7. Surface area of micropores of biochar obtained; n is the number of determinations.
Table 7. Surface area of micropores of biochar obtained; n is the number of determinations.
Initial BiomassSmicro (m2 g−1)n
BS356 ± 157
AS421 ± 115
WS409 ± 227
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Straka, P.; Cihlář, J.; Bičáková, O. Production of Syngas and Hydrogen-Rich Gas from Lignocellulosic Biomass via Ru/Al2O3 Catalyst-Assisted Slow Pyrolysis. Catalysts 2025, 15, 1033. https://doi.org/10.3390/catal15111033

AMA Style

Straka P, Cihlář J, Bičáková O. Production of Syngas and Hydrogen-Rich Gas from Lignocellulosic Biomass via Ru/Al2O3 Catalyst-Assisted Slow Pyrolysis. Catalysts. 2025; 15(11):1033. https://doi.org/10.3390/catal15111033

Chicago/Turabian Style

Straka, Pavel, Jaroslav Cihlář, and Olga Bičáková. 2025. "Production of Syngas and Hydrogen-Rich Gas from Lignocellulosic Biomass via Ru/Al2O3 Catalyst-Assisted Slow Pyrolysis" Catalysts 15, no. 11: 1033. https://doi.org/10.3390/catal15111033

APA Style

Straka, P., Cihlář, J., & Bičáková, O. (2025). Production of Syngas and Hydrogen-Rich Gas from Lignocellulosic Biomass via Ru/Al2O3 Catalyst-Assisted Slow Pyrolysis. Catalysts, 15(11), 1033. https://doi.org/10.3390/catal15111033

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