Sustainable Valorisation of Sewage Sludge via Carbon Dioxide-Assisted Pyrolysis.

The escalating volume of sewage sludge (SS) generated poses challenges in disposal, given its potential harm to the environment and human health. This study explored sustainable solutions for SS management with a focus on energy recovery. Employing CO2-assisted pyrolysis, we converted SS into flammable gases (H2 and CO; syngas). Single-stage pyrolysis of SS in a CO2 conditions demonstrated that CO2 enhances flammable gas production (especially CO) through gas phase reactions (GPRs) with volatile matter (VM) at temperatures ≥ 520 ˚C. Specifically, the CO2 partially oxidized the VM released from SS and concurrently underwent reduction into CO. To enhance the syngas production at temperatures ≤ 520 ˚C, multi-stage pyrolysis setup with additional heat energy and a Ni/Al2O3 catalyst were utilized. These configurations significantly increased flammable gas production, particularly CO, at temperatures ≤ 520 ˚C. Indeed, the flammable gas yield in the catalytic pyrolysis of SS increased from 200.3 mmol under N2 conditions to 219.2 mmol under CO2 conditions, representing a 4.4-fold increase compared to single-stage pyrolysis under CO2 conditions (50.0 mmol). By integrating a water-gas-shift reaction, the flammable gases produced from CO2-assisted catalytic pyrolysis were expected to have the potential to generate revenue of US$4.04 billion. These findings highlight the effectiveness of employing CO2 in SS pyrolysis as a sustainable and effective approach for treating and valorising SS into valuable energy resources.

Thermochemical conversion of silkworm by-product into syngas.

This study explored the valorisation of silkworm by-product, a major by-product of the silk industry (sericulture), which amounts to 16 million tonnes annually. The focus was on transforming waste into energy resources through pyrolysis under CO2 conditions. In one-stage pyrolysis, the evolution of syngas under N2 was found to be comparable to that under CO2. A notable allocation of carbon to biocrude rather than syngas was observed. The two-stage pyrolysis resulted in increased syngas production. However, achieving a homogeneous reaction between CO2 and the volatiles liberated from silkworm byproduct proved challenging. Indeed, the reaction kinetics governing CO2 reactivity was not fast although the temperature windows of the reaction were aligned in the two-stage pyrolysis. To address this issue, pyrolysis was performed using a Ni-based catalyst to expedite the reaction kinetics. Consequently, syngas formation, particularly CO formation, was significantly enhanced under CO2 conditions compared to that under N2 conditions. The syngas yield under CO2 was 36.42 wt% which was 2-fold higher than that of N2. This suggested the potential of CO2 altering the carbon distribution from biocrude to syngas. This strategy would contribute to the establishment of sustainable production of silk by converting sericulture by-product into energy/chemical resources.

Direct conversion of apricot seeds into biodiesel.

Using edible lipids for biodiesel production has been criticized, causing biodiesel production from inedible food resources to be desirable. Lipid extraction must be prioritized to produce biodiesel using an acid/base-catalyzed transesterification process, but this conversion process suffers from technical reliability. Therefore, this study introduced non-catalytic conversion of oil-bearing biomass into biodiesel. Apricot seeds were used as a model compound (oil content 44.3 wt%). The non-catalytic transesterification of apricot seed oil recovered 98.28 wt% biodiesel at 360 °C for 1 min, while alkali-catalysis of apricot seed oil recovered 91.84 wt% at 63 °C for 60 min. The direct conversion of apricot seeds into biodiesel was attempted. The trends in the yields of biodiesel from apricot seeds and seed oil obtained by non-catalytic transesterification as a function of reaction temperature were similar. The yield of biodiesel from apricot seed was 43.06 wt%, suggesting that 97.20 wt% of lipids were converted into biodiesel.

Abatement of odor emissions from wastewater treatment plants using biochar.

Odor is a critical environmental problem that negatively affects people's quality of life. Wastewater treatment plants (WWTPs) often emit various odorous compounds, such as ammonia, sulfur dioxide, and organosulfur. Abatement of odor emissions from WWTPs using biochar may contribute to achieving carbon neutrality due to the carbon negative nature, CO2 sorption, and negative priming effects of biochar. Biochar has a high specific surface area and microporous structure with appropriate activation, which is suitable for sorption purposes. Various research directions have been proposed to determine the biochar removal efficiency for different odorants released from WWTPs. According to the literature survey, the pre- and post-treatments (e.g., thermal treatment, chemical treatment, and metal impregnation) of biochar could enhance the removal capacity for the odorants emitted from WWTPs at comparable conditions, compared to unmodified biochar. The feedstock and production condition (particularly, pyrolysis temperature) of a biochar and initial concentration of an odorant markedly affect the biochar's odorant removal capacity and efficiency. Moreover, different adsorption systems for the removal of odorants emitted from WWTPs follow different adsorption models. Further research is required to establish the practical use of biochar for the mitigation of odors released from WWTPs.

Strategic use of crop residue biochars for removal of hazardous compounds in wastewater.

Crop residues are affordable lignocellulosic waste in the world, and a large portion of the waste has been burned, releasing toxic pollutants into the environment. Since the crop residue is a carbon and ingredient rich material, it can be strategically used as a sorptive material for (in)organic pollutants in the wastewater after thermo-chemical valorization (i.e., biochar production). In this review, applications of crop residue biochars to adsorption of non-degradable synthetic dyes, antibiotics, herbicides, and inorganic heavy metals in wastewater were discussed. Properties (porosity, functional groups, heteroatom, and metal(oxide)s, etc.) and adsorption capacity relationships were comprehensively reviewed. The current challenges of crop residue biochars and guidelines for development of efficient adsorbents were also provided. In the last part, the future research directions for practical applications of the crop residue biochars in wastewater treatment plants have been suggested.

Effects of Ni/Al2O3 catalyst treatment condition on thermocatalytic conversion of spent disposable wipes.

Municipal solid waste (MSW) management is an essential municipal service. Proper waste treatment is an important part of the waste management. Thermocatalytic waste upcycling has recently gained great interest and attention as a method to extract value from waste, which potentially substitutes traditional waste treatment methods. This study aims at demonstrating the potential for thermocatalytic waste upcycling using spent disposable wipes as an MSW surrogate. Two different Ni/Al2O3 catalysts were prepared, treated under two different atmospheres (N2 and CO2). The catalyst treated in N2 (Ni/Al2O3-N2) exhibited a higher surface metallic Ni site than the catalyst treated in CO2 (Ni/Al2O3-CO2). The use of the Ni/Al2O3-N2 increased the yield of gas pyrolysate and decreased the yield of byproduct (e.g., wax), compared with no catalyst and the Ni/Al2O3-CO2. In particular, the Ni/Al2O3-N2 catalyst affected the generation of gaseous hydrogen (H2) by increasing the H2 yield by up to 102% in comparison with the other thermocatalytic systems. The highest H2 yield obtained with the Ni/Al2O3-N2 was attributed to the most surface metallic Ni sites. However, the Ni/Al2O3-N2 catalyst led to char having a lower higher heating value than the other catalysts due to its lowest carbon content. The results indicated that the reduction treatment environment for Ni/Al2O3 catalyst influences thermocatalytic conversion product yields of spent disposable wipes, including enhanced H2 production. Electronic Supplementary Material: Supplementary material is available in the online version of this article at 10.1007/s11814-023-1461-8.

Selective recovery of caprolactam from the thermo-catalytic conversion of textile waste over γ-Al2O3 supported metal catalysts.

The massive generation of synthetic textile waste has drawn considerable attention. Landfilling/incineration of textile waste has been widely made. To abate the environmental burdensome from the conventional management processes, a thermo-catalytic conversion was used for rapid volume reduction of textile waste and simultaneous valorization by recovering textile monomer in this study. Stockings were chosen as a model feedstock. Because stockings consisted of nylon with other contents, different products (caprolactam (nylon monomer), imines, cyclic dimers, and azepines) were recovered. The yield of caprolactam from the thermal conversion at 500 °C was 53.6 wt%. To selectively enhance the caprolactam yield, catalytic pyrolysis was done using γ-Al2O3 supported metal catalysts (Ni, Cu, Fe, or Co). γ-Al2O3 itself increased the caprolactam yield up to 69.0 wt% via a based-catalyzed reaction of nylon depolymerization and intramolecular cyclization. Under the presence of metal catalysts, the caprolactam yield increased up to 73.3 wt%. To offer desired feature of green chemistry, CO2 was adopted as reactive gas. Under the CO2-mediated catalytic pyrolysis, caprolactam yield was enhanced up to 77.1 wt% over Cu/Al2O3 (basis: stocking mass). Based on the net content of nylon in the stockings, the yield of caprolactam was deemed 95.3 wt%. This study proves that textile waste (stocking) and CO2 are useful resources for recovery of nylon monomer, which can reduce the waste generation with simultaneous recovery of value-added product.

Environmental benefits from the use of CO2 in the thermal disposal of cigarette butts.

As the global consumption of cigarettes has increased, the massive generation of cigarette butts (CBs) has led to critical environmental and health problems. Landfilling or incineration of CBs has been conventionally carried out, but such disposal protocols have suffered from the potential risks of the unwanted/uncontrolled release of leachates, carcinogens, and toxic chemicals into all environmental media. Thus, this study focuses on developing an environmentally dependable method for CB disposal. Littered CBs from filtered/electronic cigarettes were valorized into syngas (H2/CO). To seek a greener approach for the valorization of CBs, CO2 was intentionally considered as a reaction intermediate. Prior to multiple pyrolysis studies, the toxic chemicals in the CBs were qualitatively determined. This study experimentally proved that the toxic chemicals in CBs were detoxified/valorized into syngas. Furthermore, this work demonstrated that CO2 was effective in thermally destroying toxic chemicals in CBs via a gas-phase reaction. The reaction features and CO2 synergistically enhance syngas production. With the use of a supported Ni catalyst and CO2, syngas production from the catalytic pyrolysis of CBs was greatly enhanced (approximately 4 times). Finally, the gas-phase reaction by CO2 was reliably maintained owing to the synergistic mechanistic/reaction feature of CO2 for coke formation prevention on the catalyst surface.

Applications of agricultural residue biochars to removal of toxic gases emitted from chemical plants: A review.

Crop residues are representative agricultural waste materials, massively generated in the world. However, a large fraction of them is currently being wasted, though they have a high potential to be used as a value-added carbon-rich material. Also, the applications of carbon-rich materials from agricultural waste to industries can have economic benefit because waste-derived carbon materials are considered inexpensive waste materials. In this review, valorization methods for crop residues as carbon-rich materials (i.e., biochars) and their applications to industrial toxic gas removals are discussed. Applications of crop residue biochars to toxic gas removal can have significant environmental benefits and economic feasibility. As such, this review discussed the technical advantages of the use of crop residue biochars as adsorbents for hazardous gaseous pollutants and greenhouse gases (GHGs) stemmed from combustion of fossil fuels and the different refinery processes. Also, the practical benefits from the activation methods in line with the biochar properties were comprehensively discussed. The relationships between the physico-chemical properties of biochars and the removal mechanisms of gaseous pollutants (H2S, SO2, Hg0, and CO2) on biochars were also highlighted in this review study. Porosity controls using physical and chemical activations along with the addition of specific functional groups and metals on biochars have significantly contributed to the enhancement of flue gas adsorption. The adsorption capacity of biochar for each toxic chemical was in the range of 46-76 mg g-1 for H2S, 40-182 mg g-1 for SO2, 80-952 µg g-1 for Hg0, and 82-308 mg g-1 CO2, respectively. This helps to find suitable activation methods for adsorption of the target pollutants. In the last part, the benefits from the use of biochars and the research directions were prospectively provided to make crop residue biochars more practical materials in adsorption of pollutant gases.

Upcycling textile waste using pyrolysis process.

Rapidly changing fashion trends have generated tremendous amounts of textile waste globally. Textile waste is composed of a variety of substances (natural, synthetic, organic, and inorganic fibers). The inhomogeneity and complex nature of textile waste makes recycling economically challenging. Pyrolysis is a thermochemical process that transforms waste feedstocks of an inhomogeneous and complex nature into value added products (i.e., waste upcycling). This article provides a systematic review of the currently available and investigated pyrolysis processes to upcycle textile waste (e.g., material and energy recovery). The challenges in the pyrolysis process of textile waste are discussed, and relevant future research needs are recommended. Despite these challenges, pyrolysis will be an effective end-of-life option for textile waste if continuous research and development activities are conducted.

Catalytic pyrolysis for upgrading silver grass (Miscanthus sinensis) and carbon dioxide into flammable gases.

This study proposes a sustainable hydrogen production platform using a fast-growing and inedible biomass waste, silver grass (Miscanthus sinensis). Pyrolysis of silver grass waste (SGW) was investigated using CO2 as a co-feedstock, focusing on the distribution of hydrogen in different products. When the catalyst was absent, hydrogen element distribution to H2 gas during pyrolysis of SGW at 800 °C reached 10 wt%. During pyrolysis with the Ni/SiO2 catalyst, 60.3 wt% of hydrogen was converted into H2 gas, and 7.3 wt% of hydrogen was distributed in gaseous hydrocarbons at 600 °C. Owing to the addition of CO2, CO production was promoted by the catalytic conversion of CO2 and volatile matter. Notably, CO2 has been proven to be a useful reactant for producing value-added CO. Thus, catalytic pyrolysis in the presence of CO2 can be considered as a renewable approach to produce flammable gases with the mitigation of CO2 emissions.

Sustainable valorization of styrofoam and CO2 into syngas.

Plastic is a versatile material broadly used in a variety of industries. However, the current disposal practices for plastic wastes (incineration/landfilling) add the hazardous materials into the environment. To offer a sustainable valorization platform for plastic waste, this study adopted the catalytic pyrolysis process using CO2 as a co-feedstock. A model plastic waste collected from a seaport was waste buoy (WB), which has been widely used in fishing industry. Prior to the pyrolysis tests, the exact type of plastic in WB and the thermolytic characteristics of WB were examined. Since the WB was made of polystyrene, it was mainly converted into styrene monomer (styrene), dimer (diphenyl-1-butene), and trimer (2,4,6-triphenyl-1-hexene) from pyrolysis of WB. To further valorize/detoxify styrene derivatives into value-added syngas, catalytic pyrolysis of WB was practiced using the Ni-based catalysts (2/5/10 wt% Ni/SiO2). The yield of H2 from the catalytic pyrolysis process of WB was more than one magnitude higher comparing to that from the non-catalytic one. H2 formation also increased as catalyst loading increased. When flow gas was switched from inert gas to CO2, CO gas formation was enhanced due to the chemical reactions between CO2 and styrene derivatives over Ni catalysts. Syngas (H2/CO) formation under the CO2 condition was 5 times higher in comparison to the N2 condition in catalytic pyrolyses of WB with 10 wt% Ni/SiO2. CO2 also effectively suppressed coke deposition on a Ni catalyst. This study proposes a sustainable valorization and disposal platform for used plastic waste and greenhouse gas (CO2), converting them into value-added fuel.

Valorizing plastic toy wastes to flammable gases through CO2-mediated pyrolysis with a Co-based catalyst.

Toys are discarded due to their short life cycle. Unfortunately, development of sustainable disposal platform for toy has not gained particular concern. To establish a reliable disposal platform, this study employed a pyrolysis platform to valorize plastics into value-added fuels. To confer more environmentally resilient process, CO2 was used as a feedstock to enhance the process efficiency from a perspective of the yield of flammable gases. To this end, waste toy brick (WTB) was used as a model compound. The exact types of plastics (polyacrylonitrile, polybutadiene, polystyrene, and polymethyl methacrylate) in WTB were experimentally determined. In pyrolysis of WTB, the complicated mixture of benzene derivatives was inevitably generated. To detoxify them by means of syngas (H2/CO) production, catalytic pyrolysis was performed. Co catalyst effectively induced chemical bond scissions, leading to substantially enhanced H2 formation. Also, the gas phase reactions (GPRs) between CO2 and volatile compounds over Co catalyst expedited the production rate of CO, and such CO enhancement effectively offered a chance to mitigate toxic chemical generations. The synergistic contribution of CO2 and Co catalyst enhanced syngas formation more than 25 times in reference to pyrolysis of WTB without Co catalyst. The GPRs also greatly prevented catalyst deactivation.

Disposal of plastic mulching film through CO2-assisted catalytic pyrolysis as a strategic means for microplastic mitigation.

Conventional disposal processes (incineration and landfilling) of agricultural plastic wastes release harmful chemicals and microplastics into our ecosystems. To provide a disposal platform not releasing harmful chemicals, pyrolysis of a representative agricultural plastic waste was proposed in this study. Spent plastic mulching film (SMF) was used as a model waste compound. To make pyrolysis process more environmentally benign, CO2 was used as a raw material in pyrolysis of SMF. H2 and hydrocarbons were produced from pyrolysis of SMF under the inert (N2) and CO2 conditions, because SMF is composed of polyethylene. To enhance conversion of hydrocarbons into H2, catalytic pyrolysis of SMF was conducted over Ni/SiO2. Compared to non-catalytic pyrolysis, total concentration of pyrolytic gases was enhanced up to 3.1 and 11.3 times under N2 and CO2 conditions, respectively. The gas phase reactions between CO2 and hydrocarbons led to formation of CO, which enhanced production of pyrolytic gases under the CO2 condition. Moreover, gas phase reactions resulted in less production of pyrolytic oil from CO2 condition (15.9 wt%) in reference to the N2 condition (22.6 wt%). All experimental results confirmed that CO2 and SMF can be used as useful feedstocks to produce value-added products. ENVIRONMENTAL IMPLICATION: Plastic waste used from a sector of agriculture is incinerated or/and landfilled, generating hazardous microplastic and volatile compounds into the environment. Thus, an environmentally friendly process for plastic waste materials in the agricultural industry is required. This study converted a spent plastic mulching film (SMF), broadly used for plastic greenhouse, into value-added syngas through catalytic pyrolysis. CO2 was used as a reactant. We found that concentration of CO2 was key to improve syngas formation from pyrolysis of SMF. Thus, this study suggested that CO2/SMF are used as useful feedstocks through catalytic pyrolysis, while they were previously discarded as waste materials.

Functional use of CO2 to mitigate the formation of bisphenol A in catalytic pyrolysis of polycarbonate.

The growing consumption of plastic materials has increased hazardous threats to all environmental media, since current plastic waste management methods release microplastics and toxic chemicals. As such, massive generation of plastic derived pollutants leads to significant public health and environmental problems. In this work, an environmentally sound method for valorization of plastic waste is suggested. In detail, pyrolysis of polycarbonate-containing plastic waste such as automotive headlight housing (AHH) was carried out using CO2 as a co-reactant. AHH was chosen as it discharges bisphenol A (BPA) and aromatic compounds. Under CO2 condition, emissions of BPA and its derivatives were suppressed by 14.5% due to gas phase reactions (GPRs) with CO2. Nevertheless, reaction kinetics for GPRs was not significant. To impart the GPRs, catalytic pyrolysis was done using Ni and Co-based catalysts. During catalytic pyrolysis, syngas production was more than tenfold up comparing to pyrolysis without catalyst. The expedited GPRs over catalysts resulted in the enhanced syngas formation. Total concentration of the toxic chemicals from CO2-assisted catalytic pyrolysis of AHH decreased by 86.1% and 66.7% over Ni and Co catalysts, comparing to those from N2 environment.

Valorization of aflatoxin contaminated peanut into biodiesel through non-catalytic transesterification.

Aflatoxins (AFs) are the extremely hazardous metabolites (carcinogens) that are sporadically observed in crops, and these toxic chemicals are indeed lethal to the health of living organisms including human beings. Thus, AF contaminated food waste needs to be disposed as an environmentally benign way, not releasing it into the environment. This study offered a sustainable disposal and valorization platform for AF contaminated food. Peanut was used as a model food waste, because AF is readily appeared in the peanut during its harvesting, cultivation, storage, transportation process. As the valorization platform, non-catalytic transesterification of AF contaminated peanut was employed to convert it to biodiesel (BD). From the process, lipid in AF contaminated peanut is converted into BD (95.2 wt% yield) at 365°C for 1 min. Since the boiling points of BD and AF are significantly different, this process could also resolve the separation problem of AF (180 °C) from BD (≥ 330 °C) during the transesterification reaction. As a comparison study, alkali-catalyzed reaction was done. The alkali-catalyzed one required a pretreatment process to extract peanut oil for transesterification. The highest yield was 67.8 wt% yield after 6 h of reaction at 65 °C.

Valorization of carbon dioxide and waste (Derived from the site of Eutrophication) into syngas using a catalytic thermo-chemical platform.

Global warming increases a chance of eutrophication, and such fact offers that unhygienic organic waste materials (OWMs) in water must be treated. Hence, this study laid emphasis on the thermal-chemical (pyrolysis) process to establish a rapid valorization platform for OWMs. Indeed, OWMs were collected from the eutrophication site, and OWMs were mainly comprised of lignocellulosic biomass, microalgae (cyanobacteria) and the diverse types of bacteria (commonly observed from livestock waste). In an attempt to offer more sustainable valorization route for OWMs, CO2 was used as a raw material in pyrolysis process. From the CO2-assisted pyrolysis, the conversion of CO2 and OWMs into gaseous fuel (CO) was observed. A cheap Ni-based catalyst was used in pyrolysis of OWMs as a strategic practice to promote conversion of CO2 into CO. Indeed, syngas production (38 %) was enhanced from catalytic pyrolysis over Ni/SiO2 under CO2 condition as compared to inert condition (N2).

Synergistic effects of CO2 on complete thermal degradation of plastic waste mixture through a catalytic pyrolysis platform: A case study of disposable diaper.

Consumption of diverse plastics has posed an environmental threat because their disposal practices, landfilling and incineration, release toxic chemicals and microplastics into all environmental media. Indeed, heterogeneous matrix of plastic wastes makes them hard to be disposed. As such, this study aimed to introduce an environmentally benign/reliable disposal platform for complete decomposition of plastic wastes. Pyrolysis process was adapted to convert plastics into syngas, and a disposable diaper (DD) was used as model plastic waste, because it is composed of a variety of polymeric materials. Pyrolysis of DD resulted in the formation of gaseous products and pyrogenic oils, composed of (oxygenated) hydrocarbons. Nonetheless, reactivity of CO2 as an oxidant in pyrolysis of DD was negligible. To impart the strong/desired reactivity of CO2, Ni-based catalyst was adopted. Ni catalyst enhanced H2 and CO formations 4 and 15 times more than pyrolysis without catalyst at 700 °C under CO2. The value-added syngas production was originated from the reduction of polymeric waste, and its derivatives including aromatic compounds. Thus, CO2 offered a strategic means to produce value-added chemicals and reduce aromaticity of pyrogenic products. The observations could offer an innovative way to control the fate of toxic chemicals derived from plastic pyrolysis.

Strategic disposal of flood debris via CO2-assisted catalytic pyrolysis.

Recent abnormal climate changes resulted in the dramatic alternation of rainfall and flood patterns in many countries. The massive generation of flood debris, a mixture of soil (sediment), biomass, plastic, metal, and various hazardous materials, poses various environmental and public health problems. This study suggests a sustainable technical platform to convert the hazardous materials into value-added products. CO2-assisted pyrolysis was used to thermally convert flood debris into syngas (H2 and CO). CO2 enhanced the syngas production due to gas phase homogeneous reactions (HRs) between CO2 and volatile hydrocarbons evolved from pyrolysis of flood debris. For improvement of HRs in line with enhancement of syngas production, additional thermal energy and earth abundant catalyst were used. In particular, Ni/SiO2 catalyst increased more than one order of magnitude higher syngas production, comparing to non-catalytic pyrolysis. Synergistic effect of CO2 and Ni catalyst showed nearly 50% more production of syngas in reference to catalytic pyrolysis under N2. During flood debris pyrolysis, compositional matrix of flood debris was also determined by detecting index chemicals of waste materials that cannot be identified by naked eyes. Thus, this study confirmed that CO2-assisted pyrolysis is a useful tool for conversion of flood debris into value-added chemicals.

CO2-assisted catalytic pyrolysis of cellulose acetate using Ni-based catalysts.

Cellulose acetate (CA) is one of widely used polymers for chemical and medical applications due to its versatile physico-chemical functionalities. Although its recycle is available after a deacetylation process, the recycle process releases a huge amount of wastewater. Thus, this study investigated a direct disposal process of CA with its valorization to syngas (H2 and CO) through pyrolysis. To construct more environmentally benign process, CO2 was used as a co-feedstock with CA to simultaneously convert them into syngas. Pyrolysis of CA in N2 was performed as a reference study to examine the effectiveness of CO2 on valorization of CA. Acetic acid and methyl acetate were main volatile pyrolysates (VPs) from CA pyrolysis, and the further thermal cracking of VPs resulted in syngas and CH4 formations under both N2 and CO2 conditions. To expedite syngas formations, multi-stage pyrolysis (two-stage pyrolysis) and catalytic pyrolysis were employed. With the increased thermal energy through two-stage pyrolysis, four times more production of syngas was shown, comparing to the result of a single-stage pyrolysis. With Ni catalysts, the syngas formation was the two orders of magnitude higher than the single-stage pyrolysis, and the significant enhancement of CO formation was shown in the presence of CO2 due to combined effects of CO2 and the Ni-based catalysts. This CO enhancement resulted from catalytically expedited gas phase reactions between CO2 and VPs evolved from CA. In addition, the CO2 contributed to the suppression of coke deposition on the catalyst, thereby suggesting more technical and environmental benefits of CO2 as a reactive co-feedstock of pyrolysis in reference to N2. Therefore, this study proved the direct and versatile technical platform to convert CA and CO2 into syngas.