Abstract
To enhance the catalytic performance of nickel-based catalysts and improve their efficiency in biomass pyrolysis, a nickel-based catalyst supported on a ZnZr composite carrier was synthesized using the sol-gel method. The morphological changes of the catalyst before and after the reaction were observed using X-ray diffraction, scanning electron microscopy, nitrogen gas adsorption, temperature-programmed reduction, and other methods to analyze its catalytic performance. A series of experiments were conducted to explore the optimal conditions for the catalyst’s gas production, including carrier material ratios, loading amounts, residence time, and reaction temperature. The bimetallic carrier of Zn and Zr provided a higher specific surface area, allowing the metallic nickel to enter its mesopores. The synergistic effect of the bimetallic system facilitated the catalytic activity of nickel, significantly enhancing gas production. The maximum CO and H2 production were achieved at Zn/Zr = 6/4. The catalyst achieved an optimal gas yield of 507 mL/g at a residence time of 20 min and a reaction temperature of 800 °C, demonstrating strong stability.
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Optimization of Ni/ZnZr Catalyst for Enhanced Syngas Yield in Catalytic Pyrolysis of Rice Straw
Lin Liu, Yucheng Fang, Rongyi Gao, and Jianfen Li *
To enhance the catalytic performance of nickel-based catalysts and improve their efficiency in biomass pyrolysis, a nickel-based catalyst supported on a ZnZr composite carrier was synthesized using the sol-gel method. The morphological changes of the catalyst before and after the reaction were observed using X-ray diffraction, scanning electron microscopy, nitrogen gas adsorption, temperature-programmed reduction, and other methods to analyze its catalytic performance. A series of experiments were conducted to explore the optimal conditions for the catalyst’s gas production, including carrier material ratios, loading amounts, residence time, and reaction temperature. The bimetallic carrier of Zn and Zr provided a higher specific surface area, allowing the metallic nickel to enter its mesopores. The synergistic effect of the bimetallic system facilitated the catalytic activity of nickel, significantly enhancing gas production. The maximum CO and H2 production were achieved at Zn/Zr = 6/4. The catalyst achieved an optimal gas yield of 507 mL/g at a residence time of 20 min and a reaction temperature of 800 °C, demonstrating strong stability.
DOI: 10.15376/biores.18.4.7524-7538
Keywords: Nickel-based catalyst; Synergy; Biomass pyrolysis; Catalyst activity
Contact information: School of Chemical and Environmental Engineering, Wuhan Polytechnic University, Wuhan 430023, China; *Corresponding author: whpulijfen@126.com
INTRODUCTION
The overuse of fossil fuels has resulted in severe environmental pollution. According to the “Statistical Review of World Energy” published by British Petroleum in 2022, global primary energy consumption reached 595.15 EJ in 2021, with renewable energy consumption amounting to 39.91 EJ. Despite renewable energy currently constituting only a small fraction of total energy consumption, its growth rate has been remarkable. Biomass resources, as a form of renewable energy, present a promising solution to this crisis. Unlike fossil fuels, the CO2 produced during biomass combustion is nearly equivalent to the amount of CO2 absorbed during their growth processes, thus achieving a near carbon-neutral cycle (Hu and Gholizadeh 2019). Therefore, fostering the sustainable development and utilization of biomass not only substitutes fossil fuels and reduces greenhouse gas emissions but it also lowers production costs.
Among the various types of biomass, lignocellulosic biomass is a commonly used bioenergy feedstock. It is primarily composed of cellulose, hemicellulose, and lignin (Klinghoffer et al. 2012). The challenge of improving the utilization efficiency of biomass while avoiding pollution and waste has become the core issue in biomass utilization today. Direct combustion of biomass generates a significant number of byproducts and waste, causing considerable environmental pollution. To maximize the utilization efficiency of this biomass and minimize pollution, several transformation methods have been developed, among which pyrolysis stands out (Chan et al. 2019; Hu and Gholizadeh 2019). The biofuels produced through pyrolysis are not only convenient for transportation but also significantly enhance subsequent performance and gasification processes. During pyrolysis, biomass feedstocks need to undergo pretreatment, such as mechanical compression and centrifugal grinding, to achieve a dense and well-dispersed state. Subsequently, biomass is subjected to thermal treatment in an oxygen-free environment, leading to the generation of three-phase reaction products: liquid (bio-oil), gas (pyrolysis gas), and solid (biochar). Various catalysts are commonly employed in the pyrolysis process to lower the energy barrier and enhance the tendency of the pyrolysis reactions, thereby meeting people’s requirements. Among these catalysts, supported catalysts demonstrate relatively higher catalytic efficiency (Bhoi et al. 2020).
Research on biomass pyrolysis catalysts plays a crucial role in determining the efficiency of biomass pyrolysis. Currently, nickel and cobalt are widely used as the main catalyst components. Among them, nickel-based catalysts are the preferred catalysts for biomass pyrolysis due to their high activity and low cost (Wu et al. 2013; Shen 2015). Modifying nickel-based catalysts to achieve a larger contact surface area and improve stability and activity has long been utilized in biomass tar removal. However, under high-temperature pyrolysis conditions, nickel-based catalysts tend to aggregate and became deactivated. Extensive research has demonstrated that active metals and supports are key factors affecting catalyst performance, and modifications of nickel-based catalysts typically focus on the aspects of active metals and supports. Therefore, researchers have made significant efforts to modify nickel-based catalysts, enhance their performance, and reduce coking.
ZrO2 shows promising potential as a catalyst support due to its unique interactions with electron distribution and active components. Research indicates that ZrO2 prevents catalyst cooking and enhances coke gasification (Sun et al. 2015), which has been attributed to its low concentration of Lewis acid sites and excellent stability (Walker et al. 2012). The inclusion of ZnO in catalysts improves the activity and stability of CH4 decomposition (Chen et al. 2008). Moreover, the addition of Zn to nickel-based catalysts enhances the dispersion of Ni. This effect is ascribed to the stronger tetrahedral coordination tendency between Zn2+ and O2- on the support’s surface, which is lacking in Ni2+(Loricera et al. 2012). Ye et al. (2018) investigated the impact of acidity of Ni/MCM-41 catalysts on biomass gasification tar removal and found that catalysts with higher acidity could generate higher hydrogen yields without significant sintering after gasification at 800 °C. The increased acidity also slightly promoted the formation of coke on the catalyst. Wang et al. (2022) synthesized Ni-Zr catalysts doped with Mn and Al via a one-step method for methane dry reforming. The synergistic effect of Al and Mn with Zr improved the activity of methane dry reforming and reduced carbon deposition. Characterization results revealed that the synthesized catalysts possessed a higher concentration of strong basic sites, smaller crystal grain size, and higher oxygen adsorption, which contributed to their stability. The modification methods and principles of Zn for nickel-based catalysts have also been extensively studied. Lin et al. (2022) prepared supported Ni catalysts using the impregnation-reduction method and explored the relationship between active sites and reaction pathways in Ni-catalyzed CO2 hydrogenation. The results demonstrated that alloying Ni with Zn altered the electronic structure and d-band center of Ni, weakened the interaction between Ni and CO/H2, and selectively catalyzed the reverse conversion of steam to CO, exhibiting excellent CO selectivity.
In this study, Ni/ZnZr catalysts were synthesized using the sol-gel method for catalyzing the pyrolysis of rice straw into syngas. The influencing factors in catalytic pyrolysis were investigated, and catalytic pyrolysis experiments were performed under optimal conditions to evaluate the performance of the catalyst in biomass pyrolysis.
EXPERIMENTAL
The catalyst was synthesized using the sol-gel method to achieve a high dispersion of the active components. First, ZnZr supports of different proportions were prepared by mixing 1.82 g of zinc nitrate and 2.82 g of zirconium nitrate (taking Zn/Zr = 6/4 as an example) in a beaker containing deionized water. Subsequently, the calculated amount of citric acid, ethylene glycol, and zinc nitrate solution were added, and the mixture was stirred continuously. Once the solid had completely dissolved, it was transferred to an oil bath at 95 °C and heated for 2 to 3 h until a gel-like liquid formed. The sample was then oven-dried at 105 °C for 12 h, followed by a 2-h calcination at 400 °C, resulting in the production of fresh Ni/ZnZr catalyst. Using the same method, catalysts with different nickel loading amounts (0-10 wt%) were prepared.
The reagents used for catalyst preparation in this study included nickel nitrate, zinc nitrate, zirconium nitrate, citric acid, and ethylene glycol. Detailed information regarding the required reagents and equipment during the experimental process is in Table 1.
Biomass pyrolysis feedstock was obtained from farms around Wuhan. It was pretreated before the experiment. First, the collected rice straw was washed and thoroughly dried. It was then crushed and sieved. Finally, the sieved rice straw was dried in an oven at 105 °C for 48 h to remove the effect of moisture on the experimental results The proximate analysis and ultimate analysis of the raw material rice straw are shown in Table 2.
Catalyst Characterizations
The crystal structure of the catalyst was tested using the Rigaku SmartLab SE instrument. A suitable amount of powder sample was taken and tested using an X-ray diffractometer, scanning from 5° to 90° at a rate of 5°/min. Cu-Kα radiation was employed as the light source, with a voltage and current of 40 kV and 40 mA, respectively. Additionally, the peak positions in the XRD spectrum were determined by comparing with the data cards from the International Centre for Diffraction Data (JCPDS).
The specific surface area, pore volume, and average pore size of the catalyst were measured using the Micromeritics ASAP 2460. The sample was first subjected to vacuum degassing at 120 °C for 6 h, followed by N2 adsorption-desorption isotherm measurement at 77 K. The specific surface area and pore size distribution of the sample were determined using the BET equation and BJH method, respectively.
The determination of the sample’s surface morphology was carried out using the ZEISS Ge mini 300 instrument. A small amount of sample was directly mounted on a conductive adhesive, and then gold sputter-coated using the Oxford Quorum SC7620 sputter coater at a coating current of 10 mA. Subsequently, the sample morphology was imaged using the ZEISS Ge miniSEM 300 scanning electron microscope at an accelerating voltage of 3 kV. Energy-dispersive X-ray spectroscopy mapping was performed with an accelerating voltage of 15 kV and a SE2 secondary electron detector.
The reduction temperature of different metal phases in the catalyst was determined using the temperature-programmed reduction (TPR) method, which was conducted on the Microtrac BELCAT II instrument. The catalyst was dried and pre-treated by heating from room temperature to 300 °C at a rate of 10 °C/min under a helium flow (50 mL/min) for 1 h, followed by cooling to 50 °C and then introducing a 10% H2/Ar mixed gas (50 mL/min) for 0.5 h. The desorption process was carried out by heating at a rate of 10 °C/min to 800 °C, and the reduction gas was detected using a thermal conductivity detector (TCD).
Table 1. Experimental Reagents and Equipment
Table 2. Proximate and Ultimate Analysis of Rice Straw
The experimental setup for the pyrolysis experiment consists of four components: the gas supply section, the pyrolysis reaction section, the gas collection section, and the gas processing and analysis section, as shown in Fig. 1. This apparatus was chosen for conducting relevant experiments on straw pyrolysis. Firstly, the straw and prepared catalyst are respectively placed in two quartz boats, which are then inserted into the quartz tube. Subsequently, the temperature of the tube furnace is programmed to increase at a rate of 20 ℃/min until reaching the reaction temperature. The valve of the nitrogen gas cylinder is opened, and the valve opening is adjusted to allow N2 to flow into the reaction vessel at a rate of 0.5 L/min, maintaining this condition for 30 min to establish an inert atmosphere in the system. Once heated to the reaction temperature, the furnace is pushed to the reaction zone to initiate the pyrolysis reaction process. After the pyrolysis reaction is completed, the reactor is moved to one end for cooling, and the generated gases are collected into gas bags. Finally, the collected gas is introduced into an infrared gas analyzer for analysis. To ensure experimental accuracy and minimize errors, each experimental group is conducted three times, and the average value is calculated.
Fig. 1. Experimental setup diagram: 1-Nitrogen cylinder; 2-Rotor flow meter; 3-Tubular furnace inlet valve; 4-Electric furnace; 5-Temperature control program; 6-Pressure gauge; 7-Quartz tube; 8-Tubular furnace outlet valve; 9-Gas collection bag; 10-Gas treatment device; 11-Gas analyzer
RESULTS AND DISCUSSION
To investigate the structural changes of the catalyst before and after its application, XRD characterization was performed on the fresh catalyst, as well as the catalysts used for 20 min and 100 min, as illustrated in Fig. 2. In the fresh catalyst sample, the diffraction peaks were barely discernible due to the efficient dispersion of metal particles, low crystallinity, and microcrystal sizes below the instrument’s detection limit (Taherian et al. 2020). However, after 20 min and 100 min of usage, characteristic peaks corresponding to Ni2O3, ZrO2, ZnO, and NiZr were observed. The Ni2O3 peaks appeared at 2θ=31.94° and 56.78° (JCPDS NO.14-0481), ZrO2 peaks at 2θ=30.24° and 50.25° (JCPDS NO.79-1770), ZnO peaks at 2θ=34.50°, 36.34°, 47.65°, 63.01°, 68.12°, and 69.26° (JCPDS NO.75-0576), and NiZr peaks at 2θ=42.82° and 60.37° (JCPDS NO.12-0478). By comparing the XRD patterns of the catalysts used for 20 min and 100 min, it was evident that with prolonged usage, the intensity of ZnO and Ni2O3 peaks decreased, while that of ZrO2 slightly increased, and the intensity of NiZr alloy peaks remained relatively stable. This indicates that the Ni species interacting with Zr had a certain degree of stability, while the characteristic peaks of the nickel oxide species had changed, showing that they gradually aggregated with increasing usage. Calculations using the Scherrer formula determined that the crystallite size of ZrO2 in the catalyst used for 20 min was 10.3 nm, whereas in the catalyst used for 100 min, the ZrO2 crystallite size increased to 18.2 nm. This suggests that as the catalyst is used for a longer duration, the degree of metal aggregation and the size of metal particles progressively increase.
Fig. 2. XRD patterns of fresh catalyst and after use at different times
Table 3. Physical Properties of Fresh and Used Catalysts
Table 3 presents the physical characteristics of the catalyst before and after usage, along with the N2 adsorption-desorption isotherms and pore size distribution plotted in Fig. 3. According to the classification by IUPAC, the fresh catalyst sample exhibited a Type IV isotherm, accompanied by a Type H1 hysteresis loop. Conversely, the catalyst after usage displayed a Type V isotherm and a Type H2 hysteresis loop. These results indicate that the fresh catalyst possessed cylindrical pores with the occurrence of mesopore capillary condensation (Taherian et al. 2020). In contrast, the used catalyst exhibited a connected pore effect, displaying narrower pore openings (Meirer et al. 2015). Furthermore, the specific surface area of the catalyst increased from 72.8 m2/g to 182 m2/g after usage. This significant increase can be attributed to the accumulation of Ni2O3 and ZnO nanoparticles during the pyrolysis reaction, as evidenced by the change from no peaks to peaks in the XRD spectra. (Fig. 2) (Yisup et al. 2005). By examining the pore size distribution of the catalyst, it was observed that the pore size distribution of the pre-used catalyst was relatively uniform, ranging from 2 to 30 nm. After usage, the pore size distribution extended from 2 to 50 nm, with a greater concentration in the range of 0 to 10 nm. The enlargement of pore size could be attributed to the collapse of interconnected smaller pores during the catalyst usage, resulting in the formation of larger pores. However, it is worth noting that this phenomenon only accounted for a small fraction, as most of the original pores experienced slight blockage, leading to a reduction in pore size. Importantly, the significant change in pore volume before and after catalyst usage may be attributed to the opposing effects of pore blockage, causing a decrease in pore volume, and pore collapse, resulting in an increase in pore volume, thereby offsetting each other. The decrease in average pore size in Table 3. further confirms the predominant occurrence of pore blockage.
Fig. 3. Adsorption-desorption isotherms and pore size distribution of fresh and used catalysts: (a) fresh catalyst; (b) post-use catalyst
Figure 4 illustrates the surface morphology changes of the catalyst before and after usage. Upon comparative analysis, the surface morphology variations of the catalyst before and after usage were not significant. The fresh catalyst exhibited a porous structure (Feng et al. 2017) with a relatively smooth surface, showing minimal signs of agglomeration. However, numerous small particles were observed attached within the pores. After usage, the catalyst surface became rough, exhibiting various-sized agglomerated structures. These structures included metal agglomeration and carbon deposition. As indicated by the XRD analysis, the presence of metal oxides and Ni-Zr alloy confirms the phenomenon of metal accumulation. Moreover, these rough structures increased the specific surface area of the catalyst from 72.8 to 181.9 m2/g. However, the carbon deposition covered some of the active metal sites, leading to a decrease in catalytic efficiency (Chen et al. 2004).
Fig. 4. SEM images of fresh and used catalysts: (a) fresh catalyst; (b) post-use catalyst
Figure 5 illustrates the hydrogen consumption curves of the samples after 20 min and 100 min (5 times) of usage. The 5%Ni/ZnZr catalyst subjected to thermal decomposition for 20 min exhibited two distinct reduction peaks at 285 and 710 °C. These peaks correspond to the reduction of nickel oxide (285 °C) and nickel species strongly interacting with the ZnZr support (710 °C) (Valizadeh et al. 2022). It can be observed that the peak intensity of the reduction peak significantly decreased in the sample after 100 min of usage, and the reduction temperature shifted towards lower temperatures. Similarly, the reduction temperature of the nickel species interacting with the support also shifted towards the lower temperature range at 630 °C, making it easier to reduce, but with an increase in peak intensity(Li et al. 2012). The results showed that as the usage time increased, the nickel oxide particles on the catalyst surface decreased, leading to a reduction in the active nickel particles participating in the reaction. This caused the catalytic effect to decline. On the other hand, the growing interaction between the nickel species and the support led to an increase in hydrogen consumption. This indicates that prolonged high-temperature catalytic pyrolysis promotes the formation of more alloys between the active metal and the support, highlighting the pronounced phenomenon of metal agglomeration (Klinghoffer et al. 2012).
Fig. 5. H2-TPR patterns of catalysts at different times after use
Effect of Carrier Ratio on Gas Yield
The catalyst’s influence on the dispersion of the active components and regulation of the surface morphology is vital, thereby affecting the adsorption characteristics and reaction pathways of the catalyst (Shen et al. 2020). Consequently, the impact of metal supports with different proportions of ZnZr on the catalytic performance (without adding Ni) was investigated, as depicted in Fig. 6. Overall, the gas production efficiency of the two metal composites surpassed that of the single metal. The single metal exhibited gas production of approximately 400 mL/g, whereas the bimetallic catalyst achieved a minimum gas production of 506 mL/g (Zn/Zr=4/6) and a maximum of 536 mL/g (Zn/Zr=6/4), representing a gas production increase of 26.5% and 34.1% respectively. This indicates a synergistic effect between Zn and Zr in gas production (Raveendra et al. 2018). CO production demonstrated an increasing and then decreasing trend, with the highest production occurring at Zn/Zr=2/8 and 6/4, reaching approximately 192 mL/g. H2 production follows a similar trend as CO, peaking at Zn/Zr=6/4 with a value of 202 mL/g. Compared to the absence of Zn, this represents a 64.89% increase in H2 production, which was initially 122 mL/g. However, the production of CO2 and CH4 was not significantly affected by changes on their production.
Fig. 6. Effect of different ZnZr ratios in the carrier on catalyst gas production
Effect of Nickel Loading on Gas Yield
Upon determining the appropriate support ratio, the influence of incorporating the active metal Ni on catalytic gas production was investigated, as depicted in Fig. 7.
Fig. 7. Effect of different Ni levels on catalyst gas production
Generally, the addition of Ni resulted in increased H2 production (Raveendra et al. 2018), surpassing 200 mL/g compared to the range of 153 mL/g without Ni. As the Ni content increases, H2 production initially increased and then decreased. Particularly, the addition of 5% Ni yielded a peak H2 production of 233 mL/g, representing a 51.8% increase compared to the baseline. However, the impact of Ni addition on CO production is limited, following a similar trend as H2 production. At 5% Ni addition, CO production reached its maximum value of 173 mL/g, showing a mere 13.0% increase compared to the absence of Ni. These data collectively demonstrated the more significant impact of the active metal Ni on catalytic hydrogen production. Regarding CO2 and CH4, their production demonstrates a decreasing trend. CH4 production decreased by 31.5%, from 59.0 mL/g to 40.4 mL/g, while CO2 production exhibited a more pronounced decrease, dropping by 57.7%, from 115 mL/g to 48.8 mL/g. Taking these factors into account, the addition of 5% Ni was judged to be the optimal choice (Zhang et al. 2018).
Effect of Residence Time on Gas Production
The residence time is one of the important factors determining the formation and distribution of products during pyrolysis. Increasing the residence time converts the organic vapors produced from lignocellulosic biomass into char and gas (Feng et al. 2020). Using the 5%Ni/ZnZr catalyst calcined at 400 °C, the influence of different residence times on gas product was studied, as shown in Fig. 8. With longer residence times, the gas production increased, and both CO and H2 showed an upward trend. It is worth noting that the gas production increased from 10 min to 20 min. Specifically, the CO production increased from 148 to 216 mL/g, representing a 45.8% increase, while the H2 production increased from 228 to 291 mL/g, representing a 27.3% increase. However, after 20 min, the increase in gas production becomes less pronounced, especially for H2, which remained almost constant at 30 min compared to 20 min. This may be due to the increased formation of surface carbon and larger particle size of the metal catalyst with prolonged residence time, resulting in less noticeable improvement in catalytic efficiency. From 20 min to 40 min of pyrolysis, the CO production increased from 216 to 234 mL/g, representing a 7.8% increase, while the H2 production increased from 291 to 301 mL/g, representing a 3.5% increase (Kan et al. 2016). On the other hand, both CO2 and CH4 decreased as the residence time increased. Although pyrolysis at 40 min produced more gas, it also consumed more energy, resulting in marginal improvement. From an economic perspective, a residence time of 20 min is preferable (Lovell et al. 2016).
Fig. 8. Effect of residence time on catalyst gas production
Effect of Reaction Temperature on Gas Production
With a residence time of 20 min, the effect of pyrolysis temperature on gas products from rice straw using the 5% Ni/ZnZr catalyst was investigated, as shown in Fig. 9. At low temperatures (500 °C), the gas produced during pyrolysis was mainly composed of CO2, accounting for nearly 40 vol.%. As the pyrolysis temperature increased, the CO2 concentration gradually decreased, while the concentrations of CO and H2 started to rise. The synthesis gas concentration increased from 48.8 vol.% (500 °C) to 81.0 vol.% (800 °C), representing a 32.2% increase. As for CH4, due to its low production, its concentration fluctuated slightly, reaching its maximum at 600 °C. Increasing the pyrolysis temperature from 500 to 800 °C led to a significant increase in synthesis gas production, from 104 to 163, 298, and 507 mL/g, respectively. These values correspond to a relative increase of 56.5%, 187%, and 385% compared to the synthesis gas production at 500 °C. Comparatively, under the same temperature increment of 100 °C, the pyrolysis at 800 °C demonstrated superior performance. Xie et al. (2012) also found that higher gas yields were obtained in the range of 700 to 850 °C.
Fig. 9. Effect of pyrolysis temperature on catalyst gas production
Stability Test of Catalysts
The stability of catalysts has always been a matter of concern. Even after undergoing extensive thermal cycling, the catalyst should maintain its mechanical strength as well as high activity and selectivity (Liu et al. 2022). After determining all experimental conditions, a 5%Ni/ZnZr catalyst was selected and its cyclic stability was investigated during the catalytic biomass pyrolysis process, as shown in Fig. 10. Based on the experimental results, it was found that the initial gas production of the catalyst was 626 mL/g, with a synthesis gas yield of 507 mL/g. However, with an increasing number of uses, the gas production exhibited a gradual decline. This can be attributed to the accumulation of nickel and carbon species on the catalyst surface, as well as the formation of various metal oxides observed on the catalyst surface through XRD analysis. The BET characterization revealed an increase in specific surface area, but a decrease in catalytic efficiency, suggesting that this phenomenon may be due to the excessive carbon deposition, which covered the active sites of the catalyst (Li et al. 2003). After three cycles of catalyst usage, the catalytic activity became relatively stable, with a gas production of approximately 450 mL/g and a synthesis gas yield stabilizing at around 340 mL/g. In the absence of a catalyst, the total gas production was 342 mL/g, with a synthesis gas yield of 189 mL/g. After achieving stability, the total gas production of the catalyst still exhibited a remarkable enhancement of 31.7%, while the synthesis gas yield increased by 80.3%.
In summary, the sol-gel Ni/ZnZr catalyst demonstrates excellent performance for rice straw pyrolysis under optimized conditions, holding great potential for biomass utilization. Further improving stability and antifouling ability is recommended.
Fig. 10. Stability testing of catalysts
CONCLUSIONS
- The ZnZr bimetallic carrier shows a synergistic effect in promoting gas yield compared to single metals, owing to the high specific surface area and Ni-support interaction.
- Incorporating 5 wt.% Ni significantly increased the H2 yield, while excessive Ni loading decreased gas production.
- A residence time of 20 min gave the optimal gas yield. Further extension led to marginal improvements.
- The catalyst exhibited declining activity after multiple uses due to carbon deposition and agglomeration, but it still enhanced syngas yield by 80.3% versus non-catalytic pyrolysis.
ACKNOWLEDGMENTS
The authors are grateful to “Department of Science and Technology of Hubei Province, Grant No. 2018BEC466,” and “Department of Science and Technology of Hubei Province, Grant No.2018ZYYD062,” for financial support of the present study.
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Article submitted: July 31, 2023; Peer review completed: August 19, 2023; Revised version received and accepted: September 11, 2023; Published: September 18, 2023.
DOI: 10.15376/biores.18.4.7524-7538