A series of ruthenium-doped strontium titanate (SrTiO₃) perovskite catalysts were synthesized by conventional and microwave-assisted hydrothermal methods. The structure was analyzed by X-Ray diffraction (XRD) confirming the formation of the perovskite phase with some TiO₂ anatase phase in all the catalysts. Microwave irradiation decreases the temperature and time of synthesis from 220 °C for 24 h (conventional heating) to 180 °C for 1h, without affecting the formation of perovskite. A 7 wt. % ruthenium-doped SrTiO₃ catalyst showed the best dielectric properties, and thus its catalytic activity was evaluated for the methane dry reforming reaction under microwave heating in a custom fixed-bed quartz reactor. Microwave power, CH₄:CO₂ vol. % feed ratio and gas hourly space velocity (GHSV) were varied in order to determine the best conditions for performing dry reforming with high reactants conversions and H₂/CO ratio. Stable maximum CH₄ and CO₂ conversions of ∼99.5% and ∼94%, respectively, at H₂/CO ∼0.9 were possible to reach with the 7 wt. % ruthenium-doped SrTiO₃ catalyst exposed to maximum temperatures in the vicinity of 940 °C. A comparative theoretical scale-up study shows significant improvement in H₂ production capability in the case of the perovskite catalyst compared to carbon-based catalysts.

The release of hydrogen from solid hydrides by thermolysis can be improved by nanoconfinement of the hydride in a suitable micro/mesoporous support, but the slow heat transfer by conduction through the support can be a limitation. In this work, a C/SiO₂ mesoporous material has been synthesized and employed as matrix for nanoconfinement of hydrides. The matrix showed high surface area and pore volume (386 m²/g and 1.41 cm³/g), which enabled the confinement of high concentrations of hydride. Furthermore, by modification of the proportion between C and SiO₂, the dielectric properties of the complex could be modified, making it susceptible to microwave heating. As with this heating method the entire sample is heated simultaneously, the heat transfer resistances associated to conduction were eliminated. To demonstrate this possibility, ethane 1,2-diaminoborane (EDAB) was embedded on the C/SiO₂ matrix at concentrations ranging from 11 to 31%wt using a wet impregnation method, and a device appropriate for hydrogen release from this material by application of microwaves was designed with the aid of a numerical simulation. Hydrogen liberation tests by conventional heating and microwaves were compared, showing that by microwave heating hydrogen release can be initiated and stopped in shorter times.

Gasification technology may combine waste treatment with energy generation. Conventional gasification processes are bulky and inflexible. By using an external energy source, in the form of microwave-generated plasma, equipment size may be reduced and flexibility as regards to the feed composition may be increased. This type of gasification may be combined with fuel cell technology to generate electricity for on-site microwave generation. In this paper, we present short gasification experiments with cellulose, as model biomass compound, in air plasma. In order to optimize reaction rates, gasification and plasma generation are combined in the same volume in order to expose the solids to plasma of maximum intensity. The heating value of the fuel gas yield exceeds, up to 84%, the net microwave energy transmitted into the reactor over a range of operating conditions. As the system has not been optimized, in particular regarding residence time, the results give confidence that this concept can eventually be developed into a viable small-scale decentralized gasification technology.

Microwave plasma (MWP) technology is currently being used in application fields such as semiconductor and material processing, diamond film deposition and waste remediation. Specific advantages of the technology include the enablement of a high energy density source and a highly reactive medium, operational flexibility, fast response time to inlet variations and low maintenance costs. These aspects make MWP a promising alternative technology to conventional thermal chemical reactors provided that certain technical and operational challenges related to scalability are overcome. Herein, an overview of state-of-the-art applications of MWP in chemical processing is presented (e.g. stripping of photo resist, UV-disinfection, waste gas treatment, plasma reforming, methane coupling to olefins, coal/biomass/waste pyrolysis/gasification and CO₂ conversion). In addition, two potential approaches to tackle scalability limitations are described, namely the development of a single unit microwave generator with high output power (>100 kW), and the coupling of multiple microwave generators with a single reactor chamber. Finally, the fundamental and engineering challenges to enable profitable implementation of the MWP technology at large scale are discussed.

We have demonstrated that application of simple shear flow and heat in a Couette Cell is a scalable process concept that can induce fibrous structural patterns to a granular mixture of plant proteins at mild process conditions. In particular, a Couette Cell device with 7-L capacity was employed for the production of structured soy-based meat replacers. A reduced factorial experimental design was used to find the optimum process conditions between two relevant process parameters (process time and rotation rate), while the process temperature remained constant at 120 °C. Fibre-structured products with high anisotropy indices were produced. Fibrousness is favoured at 30 ± 5 min and 25 ± 5 RPM. The up-scaled Couette Cell can be operated in higher industrial values and yield 30 mm thick meat replacers, which emulate meat. Besides, the study did not reveal any barriers for further upscaling of this concept. The flexibility in design allows production of meat alternative products with sizes that are currently not available, but could have advantages when aiming at replacement of complete muscular parts of animals, for instance, chicken breast or beef meat.

We have demonstrated that application of simple shear flow and heat in a Couette Cell is a scalable process concept that can induce fibrous structural patterns to a granular mixture of plant proteins at mild process conditions. In particular, a Couette Cell device with 7-L capacity was employed for the production of structured soy-based meat replacers. A reduced factorial experimental design was used to find the optimum process conditions between two relevant process parameters (process time and rotation rate), while the process temperature remained constant at 120 °C. Fibre-structured products with high anisotropy indices were produced. Fibrousness is favoured at 30 ± 5 min and 25 ± 5 RPM. The up-scaled Couette Cell can be operated in higher industrial values and yield 30 mm thick meat replacers, which emulate meat. Besides, the study did not reveal any barriers for further upscaling of this concept. The flexibility in design allows production of meat alternative products with sizes that are currently not available, but could have advantages when aiming at replacement of complete muscular parts of animals, for instance, chicken breast or beef meat.

We have demonstrated that application of simple shear flow and heat in a Couette Cell is a scalable process concept that can induce fibrous structural patterns to a granular mixture of plant proteins at mild process conditions. In particular, a Couette Cell device with 7-L capacity was employed for the production of structured soy-based meat replacers. A reduced factorial experimental design was used to find the optimum process conditions between two relevant process parameters (process time and rotation rate), while the process temperature remained constant at 120 °C. Fibre-structured products with high anisotropy indices were produced. Fibrousness is favoured at 30 ± 5 min and 25 ± 5 RPM. The up-scaled Couette Cell can be operated in higher industrial values and yield 30 mm thick meat replacers, which emulate meat. Besides, the study did not reveal any barriers for further upscaling of this concept. The flexibility in design allows production of meat alternative products with sizes that are currently not available, but could have advantages when aiming at replacement of complete muscular parts of animals, for instance, chicken breast or beef meat.

In the context of converting electricity into value-added chemicals, the reduction of carbon dioxide (CO₂) with hydrogen (H₂) in a surface-wave-induced microwave plasma discharge, so-called surfatron, was investigated. The effect of different input variables such as gas flow rate, feed gas composition ratio (H₂:CO₂) and specific energy input (SEI) on the reactor performance, i.e. the CO₂ conversion and energy efficiency, was assessed. A maximum CO₂ conversion of 85% is obtained when the feed gas mixture ratio (H₂:CO₂) was equal to 3. Moreover, a trade-off between CO₂ conversion and energy efficiency was clearly noticed when varying the supplied microwave power. High SEI resulted in high conversions and low energy efficiencies and vice-versa. Furthermore, the saturation of the carbon monoxide (CO) production was found at high SEI. These results were rationalized by means of a simplified reaction scheme and by optical emission spectroscopy analysis, which showed that the formation of hydrogen (H) and oxygen (O) atoms in the plasma are the dominant channels driving the reaction pathway. We also observed higher electron densities and temperatures at higher H₂ content, which may explain the high conversions achieved in the plasma reactor at high H₂:CO₂ ratios. H₂ is then not only capable of acting as a “catalyst” for CO₂ decomposition but also modifies the plasma properties, which seems to greatly enhance the potential of chemical reactions and thus the dissociation rates.

The complexity and challenges in noncontact temperature measurements inside microwave-heated catalytic reactors are presented in this paper. A custom-designed microwave cavity has been used to focus the microwave field on the catalyst and enable monitoring of the temperature field in 2D. A methodology to study the temperature distribution in the catalytic bed by using a thermal camera in combination with a thermocouple for a heterogeneous catalytic reaction (methane dry reforming) under microwave heating has been demonstrated. The effects of various variables that affect the accuracy of temperature recordings are discussed in detail. The necessity of having at least one contact sensor, such as a thermocouple, or some other microwave transparent sensor, is recommended to keep track of the temperature changes occurring in the catalytic bed during the reaction under microwave heating.