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We report a unique composite of La0.4Sr0.4Ti0.9Ni0.1O3-δ (LSTN) nanoparticles interlaced with two dimensional Ti3C2Tx (MXene) nanosheets, providing high conductivity. LSTN heterostructure synthesized by the sol-gel method produces a large oxygen vacancy and creates a variable valence state while, MXene synthesized from Hydrofluoric acid (HF) treatment resulted in a highly hydrophilic and conductive surface, thereby enhancing the charge transferability. For OER, the LSTN/MXene 66.67% electrode exhibits a benchmark of 10 mA cm−2 at a potential of 1.56 (V vs RHE) in 1 M KOH. It has exhibited the lowest Tafel slope of 44 mV dec−1 and highest mass activity (60 mA g−1 @ 1.59 V) due to quicker ions diffusion and increased available exposed area. Moreover, the efficient LSTN/MXene 66.67% electrode showed good long-term durability during a 24 h stability test at a current density of 100 mA cm−2. The strong interfacial interaction and high charge transfer among LSTN nanoparticles and 2D MXene nanosheets not only provide good structural strength to the composite but also improves the redox activity of LSTN/MXene 66.67% catalyst towards OER. This work provides improved conductive properties of perovskite by developing a composite of perovskite and MXene, that has significantly enhanced electrochemical properties of the catalyst by undergoing fast kinetics.

In the current study, the biogas production was carried out by using a semi-continuous stirring tank reactor (CSTR). Consequently, the producer biogas was scrubbed/enriched by the combination of three steps of scrubbing (H2S scrubber, packed column water scrubber (PCWS), and activated charcoal scrubber (CS)). In PCWS, the static water scrubbing (SWS) and flowing water scrubbing (FWS) techniques were employed. In SWS, the biogas was scrubbed at a defined water level for a defined time while in FWS, the biogas was scrubbed at different water/gas (w/g) flow rates. In case of SWS, removal of was up to 95% H2S removal, removal of was up to 89% CO2 removal and 97% methane refinement was achieved. While for FWS, 97% removal of H2S, 90% removal of CO2 and 97% methane refinement was achieved. Both processes proved remarkable impacts on methane refinement but FWS was found more practical because CO2 was found more soluble in flowing water as compared with static water scrubbing.

In this work, partial oxidation of methane (POM) was investigated using Mg-Ni-Al (MNA) hydrotalcite promoted CeO2 catalyst in a fixed bed reactor. MNA hydrotalcite was synthesized using the co-precipitation process, while CeO2 was incorporated via the wetness impregnation technique. The CeO2@MNA samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) technique. The catalytic activity of CeO2 promoted MNA (CeO2@MNA) for POM reaction was evaluated for various CeO2 loading kept the feed ratio CH4/O2 = 2 at 850 °C. The catalyst containing 10 wt% cerium loading (10%CeO2@MNA) showed 94% CH4 conversion with H2/CO ratio above 2.0, that is more suitable for FT synthesis. The performance of catalyst is attributed to highly crystalline stable CeO2@MNA with better Ce-MNA interactions withstand for 35 h time on stream. Furthermore, the spent catalyst was examined by TGA, SEM-EDS, and XRD to evaluate the carbon formation and structural changes during the span of reaction time.

In the recent development of structured materials, efficient and low-cost materials are highly demanding for hydrogen production. In this work, novel 3D graphitic carbon nitride hollow nanosheets (CNHNS) with controlled morphology loaded with Ru for photocatalytic hydrogen production has been investigated. Compared to CN, CNHNS improves H2 evolution of 2 times due to hollow structure with higher light absorption and proficient separation of charges within 3D structure. The highest H2 evolution was attained over 3% Ru loaded CNHNS with yield rate of 1580 μmol g−1 h−1, which was 11.9 times higher than it was evolved over CNHNS and 15.1 times more than using CN, respectively. This obvious augmented photoactivity can be assigned to boosted charges separation in hollow structure, whereas, Ru further promoted the transfer of electrons. The performance of 3D Ru/CNHNS was further increased in an externally reflected solar system, which was 1.30 times more than using photoreactor without reflector. This was evidently due to increasing light intensity inside the reactor by reflecting light, thus, promoting quantum efficiency under the same source of light. The stability results further confirm continuous H2 evolution even after six cycles. Thus, newly developed method for synthesis of hierarchical 3D hollow structures and externally reflector solar photoreactor will provide new directions for hydrogen production systems.

The catalyst has a significant role in gas processing applications such as reforming technologies for H2 and syngas production. The stable catalyst is requisite for any industrial catalysis application to make it commercially viable. Several methods are employed to synthesize the catalysts. However, there is still a challenge to achieve a controlled morphology and pure catalyst which majorly influences the catalytic activity in reforming applications. The conventional methods are expansive, and the removal of the impurities are major challenges. Nevertheless, it is not straightforward to achieve the desired structure and stability. Therefore, significant interest has been developed on the advanced techniques to take control of the physicochemical properties of the catalyst through non-thermal plasma (NTP) techniques. In this review, the systematic evolution of the catalyst synthesis using NTP technique is elucidated. The emerging DBD plasma to synthesized and effective surface treatment is reviewed. DBD plasma synthesized catalyst performance in reforming application for H2 and syngas production is summarised. Furthermore, the status of DBD plasma for catalyst synthesis and proposed future avenues to design environmentally suitable and cost-effective synthesis techniques are discussed.

A kinetic study on dry reforming of methane (DRM) in hybrid dielectric barrier discharge (DBD) plasma reactor over La2O3 co-supported Ni/MgAl2O4 catalyst has been investigated. Three different parametric effects namely specific input energy (SIE), discharge volume (VD) and feed flow rate corresponding to GHSV (h−1) are studied using the modified power-law model. The developed kinetic model indicates instantaneous conversions of CH4 and CO2 are functions of SIE, VD and GHSV. Increasing SIE linearly enhances the conversion of CH4 and CO2, while VD displays a non-linear relation with conversion and selectivity. GHSV also shows a linear relation with instantaneous CH4 and CO2 conversion and selectivity of H2 and CO. The rate constants ( k C H 4 , k C O 2 ), determined using the proposed kinetic model and various process parameters, are compared with DRM experimental results for validation. The apparent activation energy (Ea), calculated for CH4 and CO2 using modified Arrhenius equation, are = 32.6 kJ mol−1 (CH4) and Ea = 35.2 kJ mol−1 (CO2), respectively. The modified power-law model is a good preliminary description for future understanding of the overall performance of a hybrid catalytic DBD plasma reactor for DRM.

Ca-doped TiO2 films were synthesized by the modified sol-gel method and employed as the electron transport material of perovskite solar cells (PSCs). Morphological, optoelectronic, thermal, and electrical studies of thin films were investigated through XRD, RAMAN, SEM, AFM, UV-Vis, FTIR, and IV characteristics. Ca doping was detected with the help of structural properties while morphological analysis revealed that thin films based on Ca-doped titania are crack-free, homogenous, and uniformly distributed. Further optoelectronic properties have shown a promising conversion efficiency of 9.79% for 2% Ca-doped titania followed by 1% Ca-doped titania, while 3% have shown the lowest conversion efficiency among these prepared samples. The 2% an optimized doping of Ca has shown an almost two-fold increase in conversion efficiency in comparison to pristine TiO2, along with an increase in current density from 15 mA⋅cm−2 to 19.3 mA⋅cm−2. Improved energy efficiency and higher current density are attributed to faster electron transportation; moreover, the optimized percentage of Ca doping seems to be an effective approach to improve the PSCs’ performance.

Oily sludge is a hazardous waste stream of oil refineries that requires an effective process and an environment-friendly route to convert and recover valuable products. In this study, the pyrolytic conversion of the wet waste oil sludge was implemented in an autoclave pyrolyzer and a thermogravimetric analyzer (TGA) at 5°C/min, 20°C/min, and 40°C/min, respectively. The kinetic analysis was performed using model-free methods, such as Friedman, Kissenger–Akahira–Sunose (KAS), and Ozawa–Flynn–Wall (OFW) to examine the complex reaction mechanism. The average activation energy of wet waste oil sludge (WWOS) estimated from Friedman, KAS, and OFW methods was 198.68 ± 66.27 kJ/mol, 194.60 ± 56.99 kJ/mol, and 193.28 ± 54.88 kJ/mol, respectively. The activation energy increased with the conversion, indicating that complex multi-step processes are involved in the thermal degradation of WWOS. An artificial neural network (ANN) was employed to predict the conversion during heating at various heating rates. ANN allows complex non-linear relationships between the response variable and its predictors. nH, ΔG, and ΔS were found to be 191.26 ± 2.82 kJ/mol, 240.79 ± 2.82 kJ/mol, and −9.67 J/mol K, respectively. The positive values of ΔH and ΔG and the slightly negative value of ΔS indicate the endothermic nature of the conversion process, which is non-spontaneous without the supply of energy.

In this study, 10% Ni/La2O3 MgAl2O4 nano-flake catalyst was synthesized, characterized and tested in a catalytic dielectric barrier discharge (DBD) plasma for dry reforming of methane (DRM). With design of experiment (DoE), the influence of process parameters namely (1) total feed flow rate (ml min−1), (2) feed ratio (CO2/CH4), (3) input power (W) and (4) catalyst loading (g) were examined using multiple response surface methodology (RSM) through a four-factor, five-level central composite design (CCD). Second-order regression models were applied for evaluating the interaction between the process parameters and responses. Input power (X3) and total feed flow rate (X1) were the two most influential process parameters followed by catalyst loading (X4) and feed ratio (X2). The experimental and predicted results from the optimum conditions fitted-well with less than ±5% margin of error. The possible dynamic interactions between the process variables were elucidated. The optimum values are feed flow rate = 18.8 ml min−1, feed ratio = 1.05, input power = 125.6 W and catalyst loading = 0.6 g. At these conditions, the predicted CH4 and CO2 conversions are 79.86% and 84.03%, respectively. The H2 and CO yields are predicted as 41.37% and 40.47%, respectively while H2/CO ratio is above unity. The calculated EE from the RSM model is predicted as 0.135 mmol kJ−1. Low carbon deposition observed on the spent catalyst is attributed to the highly basic and oxidative nature of the La2O3 co-supported catalyst.

Dry reforming of methane (DRM) is one of the attractive methods for the utilisation of greenhouse gases (e.g., CH4, CO2) to produce valuable fuels. In the quest for an efficient development in DRM, several technologies have been practised, while dielectric barrier discharge (DBD) cold plasma technology garners special attention in the utilisation of CO2 and CH4 through DRM process due to easy upscaling opportunities and mild operating conditions. However, the low energy efficiency (EE) of DBD plasma is a distinct challenge and it offers an in-depth insight into its basic operational understandings. This review presents the overall status and current developments in DBD plasma for DRM. In the mainstream, challenges in DBD plasma technology, catalyst-plasma interactions and developments in plasma catalysts to improve the yield and selectivity of DRM have been discussed. The current status and developments in DBD reactor configuration based on reactor geometry, such as the electrode morphology, discharge gap (Dgap), discharge volume (VD) and material packing to maximise the productivity of DRM are specifically investigated. The effects of the operating parameters, such as gas hourly space velocity (GHSV), specific input energy (SIE) and feed ratio are critical for product distribution. The current status of reaction kinetics and prospects in fluid modelling of catalytic DBD plasma DRM reactor is reviewed to understand the underlying reaction mechanism. Finally, further advancements in the catalytic DBD plasma DRM has become a requisite to make it commercially viable for the successful production of valuable fuels.

The study experimentally investigated a novel approach for producing hydrogen from methane cracking in dielectric barrier discharge catalytic plasma reactor using a nanocatalyst. Plasma-catalytic methane (CH4) cracking was undertaken in a dielectric barrier discharge (DBD) catalytic plasma reactor using Ni/MgAl2O4. The Ni/MgAl2O4 was synthesised through co-precipitation followed customised hydrothermal method. The physicochemical properties of the catalyst were examined using X-ray diffraction (XRD), scanning electron microscopy—energy dispersive X-ray spectrometry (SEM-EDX) and thermogravimetric analysis (TGA). The Ni/MgAl2O4 shows a porous structure spinel MgAl2O4 and thermal stability. In the catalytic-plasma methane cracking, the Ni/MgAl2O4 shows 80% of the maximum conversion of CH4 with H2 selectivity 75%. Furthermore, the stability of the catalyst was encouraging 16 h with CH4 conversion above 75%, and the selectivity of H2 was above 70%. This is attributed to the synergistic effect of the catalyst and plasma. The plasma-catalytic CH4 cracking is a promising technology for the simultaneous H2 and carbon nanotubes (CNTs) production for energy storage applications.

The effect of quartz and alumina dielectric materials on the efficiency of dielectric barrier discharge (DBD) cold plasma reactor using different configurations for dry reforming of methane (DRM) has been investigated. The performance of dielectric materials was analysed at different feed ratios, gas hourly space velocity (GHSV, h−1) and specific input energy (SIE, kJ L−1). In both reactors, the main products detected were CO and H2 with considerable amounts of C2H6. Alumina reactor prevailed in performance and the maximum conversion achieved was 74% and 68% for CH4 and CO2, respectively at GHSV (92 h−1) feed ratio (1:1), SIE (370 J ml−1) and discharge volume (VD = 15.7 cm3). The CO/H2 ratio and yields were also higher in alumina than the quartz reactor under the same experimental conditions. Furthermore, different reactor configurations displayed a significant impact in the performance of DBD plasma. Increasing discharge volume (VD) enhanced the conversion and selectivity for both dielectrics. The energy efficiency (EE) was of 0.085 and 0.078 mmol kJ−1 for alumina and quartz, respectively. The high EE in alumina reactor was evidently due to higher dielectric constant, which exhibited enhancement in power dissipation, discharge energy and reactor temperature. Stability test conferred alumina DBD plasma reactor performed better than the quartz.

Co/TiO2–MgAl2O4 was investigated in a fixed bed reactor for the dry reforming of methane (DRM) process. Co/TiO2–MgAl2O4 was prepared by modified co-precipitation, followed by the hydrothermal method. The active metal Co was loaded via the wetness impregnation method. The prepared catalyst was characterized by XRD, SEM, TGA, and FTIR. The performance of Co/TiO2–MgAl2O4 for the DRM process was investigated in a reactor with a temperature of 750 °C, a feed ratio (CO2/CH4) of 1, a catalyst loading of 0.5 g, and a feed flow rate of 20 mL min−1. The effect of support interaction with metal and the composite were studied for catalytic activity, the composite showing significantly improved results. Moreover, among the tested Co loadings, 5 wt% Co over the TiO2–MgAl2O4 composite shows the best catalytic performance. The 5%Co/TiO2–MgAl2O4 improved the CH4 and CO2 conversion by up to 70% and 80%, respectively, while the selectivity of H2 and CO improved to 43% and 46.5%, respectively. The achieved H2/CO ratio of 0.9 was due to the excess amount of CO produced because of the higher conversion rate of CO2 and the surface carbon reaction with oxygen species. Furthermore, in a time on stream (TOS) test, the catalyst exhibited 75 h of stability with significant catalytic activity. Catalyst potential lies in catalyst stability and performance results, thus encouraging the further investigation and use of the catalyst for the long-run DRM process.

Catalytic and thermal cracking of polypropylene was performed in a batch reactor. Effect of hydrochloric acid activation on kaolin clay, effects of catalysts (acid-activated clays), promoter (5 wt% Ni), and cracking temperatures on the liquid oil yield were investigated. Results show optimized liquid yield (71.9%) obtained at 470°C with kaolin clay activated with 3 M HCl. Acid-activated catalysts were analyzed using XRD and the results reveal the reduction in peaks’ intensities. Weight loss of polypropylene was investigated by thermogravimetric analysis. FTIR and GCMS techniques were employed to analyze the liquid products.