Methane is a greenhouse gas 28 times more potent than CO2, with wetlands and agricultural practices accounting for 32 and 38% of total natural and anthropogenic methane emissions, respectively. The diluted and distributed nature of these emissions makes them hard to mitigate. Therefore, effective mitigation techniques are essential to reduce its impact, with catalytic oxidation emerging as a promising solution. In this study, methane oxidation over transition metal oxides is investigated to remove low-concentration CH4 due to its high efficiency and low secondary pollution. The catalytic performance of different transition metal oxides (Co, Ni, and Mn), including single and binary metal oxides, was investigated under controlled conditions to facilitate direct comparison. The experimental investigation revealed that Co3O4–MnxOy and Co3O4 catalysts achieved a 90% methane conversion rate at 330 and 380 °C. The high surface area and small crystallite size of Co3O4–MnxOy increase the exposure of active sites, while the synergistic effect of Mn and Co promotes oxygen vacancy formation. In contrast, Co3O4 benefits from a high density of surface oxygen vacancies and an optimal acid–base balance, enabling intermediate stabilization and rapid redox cycling. By linking catalytic performance to structural features such as surface morphology, oxygen vacancies, acidity–basicity, and crystallite structures, this study provides insights into the reaction mechanisms governing methane oxidation.

Lubrication base oils are produced in hydrotreaters using a wide range of feedstocks and process conditions. When either the feedstock or process conditions are changed, the catalyst activity appears to change requiring several days of operation to reach a stable activity state. In the present study, a feedstock switch is performed in a pilot hydrotreating unit using light and heavy vacuum gas oils (LVGO and HVGO), to investigate the transient reactor's behaviour and catalyst activity. To decouple the hydrodynamic and the kinetic effects, a tracer study was conducted utilizing standard refinery analytical methods. The obtained transient data was described and explained by a simplified mathematical model accounting for the hydrodenitrogenation (HDN) and hydrodearomatization (HDA) reactions. The experimental results indicate that the sequence of feedstock switch impacts the time to steady state with the LVGO to HVGO switch reaching a steady state after 40 h while the HVGO to LVGO required only 20 h. Moreover, the average boiling point (T50) was found to be a suitable tracer for characterizing the reactor's hydrodynamics. The developed model exhibited a good fit to the transient data obtained from the pilot unit. It was shown that the dynamics of the HDA closely follow those of HDN. Moreover, the adsorption rate coefficient and the HDN reaction rate coefficient were 30 % and 12 % higher, respectively, for the LVGO compared to the HVGO. In conclusion, this study provides a quantitative understanding of the feedstock switch supporting the optimization of hydrotreaters operation.

The selection of appropriate catalysts is critical for the efficient operation of hydrotreaters, due to the diverse types of reactions inherent to the process. In this study, various Type I and Type II sulfided NiMo/γ-Al<inf>2</inf>O<inf>3</inf> hydrotreating catalysts were prepared using chelating agents and support modification, and the apparent activity differences were evaluated using step response experiments. The experiments were conducted in a trickle bed reactor at 300 °C and 120 barg using phenanthrene and carbazole as model compounds while the apparent activities were elucidated using dynamic reactor modelling. It was found that the addition of citric acid to the impregnation solution to chelate the Ni leads to an average 30% increase in the active site density for hydrogenation (HDA) and hydrodenitrogenation (HDN), without significantly affecting the reaction rate coefficients suggesting similar activity per active site. Phosphorus modification of the support, however, results in larger reaction rate coefficients for both hydrogenation of phenanthrene as well as adsorption and reaction coefficients for carbazole, resulting in more active catalysts both for HDA and HDN. This enhanced activity is accompanied by increased selectivity to HDN suggesting that catalysts exhibiting higher activity for HDA reactions are more susceptible to inhibition by organonitrogen compounds. In addition, dynamic activity testing indicated that catalysts with superior HDN activity attain their new steady state in the shortest time. Thus, the selection of catalysts for efficient hydrotreater operation necessitates activity testing under dynamic conditions to account for competing and inhibitory reactions, rather than relying solely on steady-state activity. Such an approach, allows for the elucidation of the differences in HDA and HDN activity, providing valuable insights to support the catalyst selection process.

The storage and distribution of H2 represent major challenges for its widespread utilization. Liquid organic hydrogen carriers (LOHC), such as methylcyclohexane (MCH), offer a promising alternative by enabling H2 delivery through dehydrogenation to toluene. Although Pt-based catalysts are the state of the art for this process, this study investigates Ni–Cu catalysts as non-noble metal alternative. For this purpose, two γ-Al2O3–supported bimetallic Ni-Cu catalysts were prepared at Cu/Ni atomic ratios of 0.25 and 0.56 and their activity and selectivity towards toluene were evaluated and compared with monometallic Pt (0.6 wt%), Ni (12.8 wt%) and Cu (20.0 wt%) γ-Al2O3–supported catalysts. The experimental evaluation was carried out in a fixed-bed reactor at a temperature and pressure of 320 °C and 1.5 bara respectively, and at a weight hourly space velocity of 2.2 h−1. Characterization of the synthesized Ni–Cu catalysts indicated the absence of alloy formation under the synthesis conditions. Experimental results indicated that the bimetallic catalysts exhibited increased activity and selectivity to toluene compared to the monometallic counterparts (i.e. Ni, Cu). A positive correlation was observed between copper addition and MCH conversion, with the Ni–Cu catalyst having a Cu/Ni ratio of 0.56 exhibiting a sevenfold increase compared to the monometallic Ni (7% compared to 1%) at the studied conditions. Nevertheless, the performance remained considerably lower than that of Pt-based catalysts, which achieved 33% MCH, under the conditions studied. Moreover, the selectivity towards toluene was observed to increase with time on stream stream, initially reaching 88% for Cu/Ni = 0.56, comparing with 60% and 85% for Ni/γ-Al2O3 and Pt/γ-Al2O3 respectively. This results suggests that Cu addition can inhibit the hydrodealkylation of toluene, thereby suppressing the dehydrogenation selectivity of unpromoted Pt catalysts. The enhancement in activity of NiCu catalysts is plausibly attributed to the Ni–Cu interactions at the interface, wehreas the improvement in selectivity is considered to arise from the preferential occupation of the C–C cleavage sites on Ni by Cu. However, catalyst stability was not improved by Cu addition with the deactivation rate being positively correlated with Cu content.

Absorption by aqueous potassium carbonate is gaining renewed interest as a post-combustion carbon capture technology due to its benign chemistry and low regeneration duty. In this work, we present new experimental data on the absorption rate of CO<inf>2</inf> into aqueous K<inf>2</inf>CO<inf>3</inf>. We performed absorption experiments on 25 wt% K<inf>2</inf>CO<inf>3</inf> at a temperature of 313–358 K and solvent loadings up to 70%, using a thermostatted, stirred batch reactor. A stagnant film model accounting for all reactive species was used to derive the second order rate constant (k<inf>2</inf>) for the reaction between CO<inf>2</inf> and OH⁻. The role of the reaction was found to diminish with increasing solvent loading due to a decrease in the hydroxide concentration, whereas the k<inf>2</inf> was instead found to increase with the solvent loading. To explain this behavior we developed an ion-contribution model that relates k<inf>2</inf> to the ionic composition of the solvent. The model describes the experiments over the whole range of data with good accuracy. The results of this work are relevant for industrial applications of aqueous K<inf>2</inf>CO<inf>3</inf> where the absorption process is operated at high solvent loading to minimize regeneration duties.

Red mud is a hazardous waste of the alumina refining process, with 1–1.5 tons generated per ton of alumina produced. This study presents a first-of-its-kind understanding of a biomass-based pathway for recovering iron from red mud. Simultaneous red mud reduction and biomass gasification (SRG) is proposed as a viable pathway to produce zero-valent iron. This metallic iron can potentially be recovered by weak magnetic separation and integrated into the iron-making industry. The steps of the red mud-biomass phenomena were investigated through thermogravimetric analysis followed by XRD characterization. Complete reduction from Fe³⁺ to Fe⁰ was achieved at temperatures near 900 °C and verified by XRD, XPS, and FTIR. Bench-scale SGR experiments were also performed to survey the compositions of gaseous and tar products. Bench-scale SRG experiments confirmed increased syngas (CO and H₂) production and demonstrated the tar-cracking catalytic activity of red mud.

Hydrogen is a versatile energy vector for a plethora of applications; nevertheless, itsproduction from waste/residues is often overlooked. Gasification and subsequent conversion ofthe raw synthesis gas to hydrogen are an attractive alternative to produce renewable hydrogen. Inthis paper, recent developments in R&D on waste gasification (municipal solid waste, tires, plasticwaste) are summarised, and an overview about suitable gasification processes is given. A literaturesurvey indicated that a broad span of hydrogen relates to productivity depending on the feedstock,ranging from 15 to 300 g H2/kg of feedstock. Suitable gas treatment (upgrading and separation) isalso covered, presenting both direct and indirect (chemical looping) concepts. Hydrogen productionvia gasification offers a high productivity potential. However, regulations, like frame conditions orsubsidies, are necessary to bring the technology into the market.

In this study time-resolved char conversion and alkali release under steam gasification conditions were investigated using a fixed bed reactor. The behaviour of an industrial char and chars produced from straw and furniture waste was investigated. For woody chars, an increase in gasification reactivity is observed together with a notable alkali release as the gasification approaches completion (degree of conversion > 0.8). In contrast, straw char exhibited a decrease in conversion rate and alkali release throughout the gasification process, attributed to the formation of catalytically inactive potassium silicates inhibiting the catalytic role of alkali. Aerosol particles in the 0.01–22 µm size range are emitted during the char conversion. A fraction is formed by nucleation of alkali compounds and other condensable gases. A wide particle distribution that extends over the whole size range is also observed, and the particles are likely to consist of solid char fragments. The study concludes on the importance of alkali release, illustrating the difference in alkali release pattern for high and low ash char.

The conversion of biomass-derived oxygenates over zeolite catalysts constitutes a challenge for the efficient production of bio-based chemicals and fuels due to difficulty in controlling the selectivity and high coke formation of such reactions. This is partly attributed to the microstructure of zeolite catalyst which affects the conversion and selectivity of products derived from biomass-derived oxygenates. In this study, the conversion and deactivation characteristics of three different model oxygenates found in biomass bio-oil (namely, acetol, furfural and guaiacol) over ZSM-5 zeolites of varying acidity, pore and crystal size prepared with bottom-up and top-down approaches were evaluated using a fixed bed microreactor at atmospheric pressure and a space velocity of 5 h−1 at a temperature range of 450–650 °C. Analysis of the experimental results indicates that the optimum temperature for such conversions is in the vicinity of 600 °C allowing for complete conversion of the compounds and high resistance to coking. The mechanisms of those conversions are discussed based on the obtained results. In general, crystal size and mesoporosity induce easier access to active sites improving mass transfer but also alter the location type, and strength of acid sites allowing for higher yields of primary and intermediate products such as olefins.

Bed materials provide efficient heat transfer and catalytic function in the thermochemical conversion of biomass, but their interactions with the fuel remain incompletely understood. In this study, the effects of bed materials on alkali release and fuel conversion during wood pyrolysis and CO2 gasification are investigated by online alkali detection combined with thermogravimetric analysis. The investigated bed materials include silica, sea sand, alumina and the natural ores olivine, ilmenite and dolomite. Only dolomite has a significant effect on fuel mass loss and alkali release during wood pyrolysis, while all bed materials influence char reactivity and alkali release during gasification. Sea sand, alumina and dolomite enhance the char gasification during the whole or most of the gasification process, which is related to alkali migration from the bed materials. All bed materials affect char reactivity and alkali release when the conversion approaches completion, and small amounts of some bed materials reduce the alkali release by an order of magnitude. The findings can be understood based on the chemical composition of the different materials. Silicon-rich materials reduce the levels of catalytically active alkali by formation of stable alkali silicates, and a similar explanation applies for ilmenite that captures alkali efficiently. Magnesium and calcium in contrast promote alkali release through their influence on alkali silicate chemistry. Analysis of char surfaces using scanning electron microscopy with energy dispersive spectroscopy indicates that low amounts of several elements are transferred from the bed material to the char where they may be directly involved in the char conversion process. The transferred elements are specific for each bed material and relates to their chemical composition. Mechanisms for material exchange between bed material and char are discussed.