Packed beds are among the most used reactors in many sectors of chemical industries. In this work, the aim was to develop a general dynamic heterogeneous multiscale model for continuous packed bed reactors, by using experimental data to improve the accuracy of mass transfer modelling. Arabinose oxidation to arabinoic acid with molecular oxygen was used as a case study. Experiments were performed in a continuous reactor system composed of a packed bed connected with a buffer tank for allowing recycling of the liquid phase and precise pH control. The packed bed was filled with laboratory prepared gold on alumina (3 %) catalyst extrudates. Various liquid flowrates were screened (150 mL/ min, 200 mL/min and 250 mL/min). The obtained experimental results were used to estimate more accurately the gas-liquid mass transfer coefficient, which was implemented in the model by using the gPROMS Model Builder. The effect of different liquid flowrates on the reactor performance was evaluated. The results showed that complete arabinose conversion can be obtained in all the cases. However, a high conversion was achieved faster in case of higher liquid flowrates (9.9 h for the 250 mL/min, 10.4 h for the 200 mL/min and 10.95 h for 150 mL/min), which agreed with our experimental discoveries: the reason is that the high flow rate suppresses the external mass transfer resistances at the gas-liquid interface and around the catalyst extrudates.

Solventless hydrodeoxygenation of dihydroeugenol was investigated in a continuous reactor at 300 degrees C under 30 bar over different nickel-iron catalysts, prepared using a two-step impregnation method. The following catalysts were studied: mesoporous FeNi/Al2O3, FeNi/SiO2 and FeNi/H-MCM-48 as well as microporous FeNi/HBeta-300, FeNi/H-Beta-38, FeNi/H-Y-5.1, FeNi/H-MCM-48 and FeNi/USY-30. The catalysts were characterized by SEM coupled with energy dispersive X-ray analysis, Mossbauer and X-ray absorption spectroscopy, hydrogen TPR, X-ray diffraction, TEM, nitrogen physisorption and FTIR pyridine adsorption. DFT calculations were performed to elucidate the role of Fe and Ni. The results revealed that FeNi/Al2O3 was the most active and stable in dihydroeugenol hydrodeoxygenation. Complete conversion of dihydroeugenol was obtained and the yield of the main product propylcyclohexane was varying in the range 84-88 %. FeNi/Al2O3 catalyst exhibited 3.4 nm metal particles and contained FeNi alloy particles with the fcc metallic structure. No deactivation was observed for FeNi/ Al2O3 during 5 hours time-on-stream due to the presence of Ni-rich particles with iron-enriched outer surface confirmed by EXAFS. Fe was shown to be responsible for deoxygenation, while Ni promotes hydrogenation. Catalyst deactivation was observed for all other catalysts except for FeNi/Al2O3 with increasing time-on-stream under the same reaction conditions due to their higher Br & oslash;nsted to Lewis acid site ratio and larger average metal particle size in comparison to FeNi/Al2O3.

The catalytic oxidation of arabinose to arabinonic acid was investigated in a recycled packed bed reactor to address pH control issues in continuous processes. Packed bed reactors are pivotal in the valorization of biomass, making the shift from batch to continuous systems critical for industrial applications. The setup used 2.1% Au/γ-alumina catalyst extrudates and incorporated a tandem reactor system with a liquid recycling loop to maintain a controlled pH of 8, ensuring optimal reaction conditions. Experiments were conducted at a reactor temperature of 70 °C, with liquid flow rates of 40 and 70 mL/min. The results demonstrated that the liquid flow rate significantly influences the arabinonic acid production, particularly during the initial stages, where the overall reaction rate is flow rate dependent. The higher flow rate (70 mL/min) resulted in faster arabinonic acid formation, attributed to increased reactant-catalyst contact and improved mass transfer, which also mitigated potential catalyst deactivation. These findings highlight the importance of flow rate optimization for enhanced sugar acid yields in continuous reactor systems and underscore the need for further research to optimize the reactor design and operation.

Data on the activity of Fe-containing Fischer-Tropsch catalysts doped with Cu, Co, and K deposited on attapulgite, as well as with different Cu:Fe ratios (3:17, 12:8 or 17:3), have been established in the synthesis of C2+ alcohols from synthesis gas (H2:CO=1; 2) to produce sustainable aviation fuel (225–300 °C, 30 bar). It was found that the joint introduction of Cu, Fe, Co and K provides a higher yield of C2+ alcohols, the selectivity of which increases with increasing proportion of Fe and temperature (H2:CO=1), reaching 90% over 3Cu17FeCoK/attapulgite at CO < 10% conversions. It is noted that the higher activity of 3Cu17FeCoK along the route of synthesis of C2+ alcohols is apparently associated with a higher content of highly dispersed phases of Fe0; Fe 3 O 4 (XRD) and a uniform distribution of metals on the surface (TEM), providing effective interphase contact.

The conversion of syngas into higher alcohols was examined using bimetallic Rh-Co, Rh-Cu, and multimetallic RhCuPd catalysts, all of which were supported on ZrO2. This process was also studied using a MnOx-promoted Rh/SiO2 catalyst. These experiments were conducted within a temperature range of 225-300 degrees C, under a pressure of 30 bar, and with a H2/CO ratio of 2. The catalysts were characterized using a variety of physicochemical methods, including Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Carbon Monoxide Diffuse Reflectance Infrared Fourier Transform Spectroscopy (CO DRIFTS). The Rh particle sizes in the fresh catalysts were found to be less than 3 nm. The Rh-Co catalyst supported on ZrO2 exhibited the highest selectivity to ethanol, achieving 38 % at a CO conversion rate of 58 % at 275 degrees C. This catalyst also demonstrated a chain growth probability of 0.35 for alcohols. A slightly higher chain growth probability was observed with the Rh-MnOx/SiO2 catalyst, although this also resulted in the formation of substantial amounts of acetic acid. Interestingly, this acetic acid could be converted into ketones when RhMnOx was used in conjunction with Pd/ZrO2.

Synthesis of higher alcohols from syngas (H2:CO ratio 2 and 1) was performed at 225-300 degrees C and 30 bar over copper, iron and cobalt containing catalysts supported on attapulgite and promoted with potassium. The Cu:Fe ratio was varied to study its influence on the syngas conversion and product distribution. It was found that while the copper rich catalyst 17Cu3FeCoK/attapulgite resulted in higher selectivity to the undesired alkanes with methane as the major one, the iron rich 3Cu17FeCoK/attapulgite was more selective towards alkenes. Selectivity to CO2 was independent on the Cu:Fe ratio tested in this work. With the higher H2:CO ratio (i.e. 2) selectivity to the liquid products increased with the increasing iron content. Moreover, a higher iron content in the catalyst improved formation of higher alcohols while the alpha-value reflecting the chain growth probability was more or less independent on the catalyst type.

Co-processing of n-hexadecane with lignin derived isoeugenol as a model compound was investigated in this work using low-cost mono-and bimetallic iron and nickel supported on H-Y-5.1 zeolite. Different Fe-Ni metal ratios in the catalyst led to different reaction rates of processes and product distribution. The presence of just 0.26 wt% isoeugenol in the mixture with n-hexadecane made hydroisomerization-hydro cracking of the latter two-fold less active. Catalysts with smaller metal particle sizes, lower than 6 nm were more efficient pointing out on structure sensitivity. Extremely high activity in co-processing was obtained over 2 wt% Fe - 8 wt% Ni/H-Y-5.1 catalysts with the median metal particle size of 4.6 nm and metals-to-acid site ratio of 8.6. Fe catalyst were much less active in isoeugenol hydrodeoxygenation, while high cracking activity of hexadecane was observed in the presence of Ni. Alkylation of n-hexadecane was a feature of 8 wt% Fe - 2 wt% Ni/H-Y-5.1, whereas, over the 5 wt% Fe - 5 wt% Ni/H-Y-5.1 bifunctional catalyst no undesired oxygen-containing cyclic products were detected. This catalyst exhibited the highest hydrogen consumption according to temperature programmed desorption, which can serve as a marker for efficient hydrodeoxygenation. The spent catalysts contained ca 40 wt% of coke with predominantly aliphatic species. (c) 2023 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Oxidation of arabinose was investigated in a tandem reactor system comprising a fixed bed of gold catalysts supported on extrudates or solid foams and a stirred tank allowing operation under constant pH of 8. Powder catalyst containing 3 wt% Au deposited on gamma-alumina was extruded with gamma-alumina and attapulgite or sepiolite as a binder or deposited on the solid open-cell aluminum foam after anodic oxidation pretreatment. Alternatively, deposition precipitation of gold with urea from HAuCl4 precursor was done directly on the extruded support or the solid foam. The presence of gold was essential for catalytic activity which in the applied reactor set-up was strongly limited by mass transfer. Arabinose was rather selectively (ca. 90-95% at full conversion) oxidized to arabinonic acid giving besides arabinolactone other by-products. A mathematical model was developed for the open foam catalyst structures and the extrudates, comprising intrinsic kinetics deduced from batch experiments and the mass transfer within the solid catalyst.

Although catalyst shaping by extrusion has been industrially applied for decades to suppress the pressure drop, much less emphasis was put on fundamental understanding of extrusion for catalytic pastes and its effect on the properties of the final catalyst bodies. During recent years intensive research efforts have been put on synthesis of extrudates by systematically varying different synthesis parameters, methods of metal modifications, different types of binders and correlating extrudate properties with their performance in several catalytic reactions. The synthesis method of extrudates can have a large impact on properties, relevant for catalysis, including acidity/basicity, the metal location and the particle size as well as textural properties, which can differ from the properties of the corresponding powder catalysts. Furthermore, a binder can interact with the support changing physico-chemical and catalytic properties. The current review summarizes recent developments related to shaping of catalysts by extrusion addressing also such advanced methods to investigate diffusion of liquid reactants inside the extrudates and interconnectivity of pores, as pulse gradient field NMR spectroscopy and fluorescent probe analysis respectively.

Optimization of bifunctional Ni catalysts was performed to enhance the catalytic performance in the one-pot synthesis of commercially valuable menthol from citral. The effect of nickel precursors (nitrate, chloride, acetate, and sulfate) and the addition of bentonite clay was investigated in citral transformations in a batch reactor at 70 degrees C and 10 bar hydrogen, demonstrating higher activity for the Ni-H-beta-38-bentonite composite derived from a nickel nitrate precursor, which can be attributed to a higher surface area, optimal Bronsted to Lewis acidity and metal particle size, as well as the egg-shell distribution of Ni particles. H-beta-38 impregnated with nickel nitrate, followed by calcination and reduction, was shaped with bentonite as a binder to give extrudates for exploring the citral transformations in the trickle-bed reactor at 50-70 degrees C and 10 bar hydrogen. The highest selectivity to the desired menthols of 45% was obtained with 70% stereoselectivity to the menthol isomer at 70 degrees C. The apparent activation energy for citral transformations to menthols of 18.6 kJ/mol indicated the presence of mass transfer limitations. Catalytic activity was linked with the physical-chemical properties, which were characterized by transmission electron microscopy, X-ray diffraction, temperature -programmed reduction, Fourier transform infrared spectroscopy with pyridine, N2 physisorption, and inductively coupled plasma- optical emission spectrometry methods.

Dry reforming ofmethane (DRM) is a promising method to utilizetwo greenhouse gases, such as CH4 and CO2, toproduce synthesis gas. In the current work, both monometallic Ni andbimetallic Ni-Fe catalysts with different Fe/Ni molar ratios,synthesized by solution combustion synthesis (SCS) in DRM, were investigatedusing a feed ratio of CH4/CO2/Ar of 1:1:1 at600-900 & DEG;C. The catalysts were characterized by severalphysicochemical techniques such as X-ray diffraction (XRD), scanningelectron microscopy energy-dispersive X-ray (SEM-EDX) spectroscopy,transmission electron microscopy (TEM), CHNS, N-2 physisorption,H-2-TPR, O-2-TPO, NH3-TPD, and thermogravimetricanalysis (TGA). One of the highest hydrogen yields of 81% was obtainedat 93% conversion of CH4 and 94% conversion of CO2 for the bimetallic 15Ni-5Fe-30Al catalyst, which contained,according to XRD, NiAl2O4 spinel and metallicNi phases. The spinel phase was decomposed during the reaction, whilethe Ni3Fe alloy was formed. Catalysts with a higher Fe/Niratio exhibited lower conversion and contained an inactive FeAl2O4 spinel. Rather stable yields of CO and H-2 were obtained in an experiment with 20 h time-on-stream.

ABSTRACT This review summarizes the recent studies on the synthesis of secondary amines by one-pot amination of aldehydes and ketones over heterogeneous catalysts. Amines are widely applied as the key intermediates in chemical industry for the synthesis of various commodities such as agrochemicals, drugs, detergents, lubricants, food-additives and polymers. Direct catalytic reductive amination of carbonyl compounds was considered which generally includes two steps: (i) formation of imines by interactions of aldehydes or ketones with amines, and (ii) subsequent hydrogenation of imines. Synthesis of secondary amines from carbonyl compounds and amines generated in situ under reaction conditions from their progenitors, e.g., respectively, alcohols or nitro-compounds, is also discussed in detail. Recent progress in application of hydrogen sources alternative to gaseous H2, such as formic acid, NaBH4, CO and water, favored development of metal-free catalysts including solid acid catalysts. The review addresses the scope of the amination reaction with aldehydes/ketones and nitro/amine compounds of different structure, the effect of the solvent, reaction conditions and catalyst properties. In addition, catalyst regeneration and reuse, kinetic regularities and kinetic modeling with an emphasis on the continuous mode of one-pot amination have been systematically summarized and discussed. It is suggested that the future work should focus on revealing the role of the catalytically active sites addressing their acid–base properties and the correlation between catalyst properties and the reaction performance, elucidating kinetic parameters and designing feasible reactor system for further industrial implementation.

A set of low-cost monometallic Fe, Ni, and bimetallicFe-Nibifunctional H-Y-5.1 catalysts with different metal ratioswere synthesized by sequential incipient wetness impregnation. Thecatalysts were characterized in detail by N-2 physisorption,Fourier transform infrared spectroscopy with pyridine, inductivelycoupled plasma optical emission spectroscopy, X-ray diffraction (XRD),transmission and scanning electron microscopy (TEM-SEM), magicangle spinning nuclear magnetic resonance, X-ray photoelectron spectroscopy(XPS), Mo''ssbauer spectroscopy, magnetic measurements, temperature-programmedreduction (TPR), and X-ray absorption spectroscopy (XAS). The resultsrevealed that introduction of Fe led to a decrease of strong acidsites and an increase of medium Bronsted acid sites, while introductionof Ni increased the number of Lewis acid sites. The particle sizeof iron was approx. 5 nm, being ca. fourfold higher for nickel. XPSdemonstrated higher iron content on the catalyst surface comparedto nickel. Both Mo''ssbauer spectroscopy and magnetic measurementconfirmed the ferromagnetic behavior of all catalysts. In addition,the results from XRD, TEM, XPS, XAS, and magnetization suggested strongFe-Ni nanoparticle interactions, which were supported by modelingof TPR profiles. Catalytic results of the co-processing of fossilfeedstock with lignin-derived isoeugenol clearly showed that bothproduct distribution and activity of Fe-Ni catalysts stronglydepend on the metals' ratio and their interactions. Key propertiesaffected by the Fe-Ni metal ratio, which played a positiverole in co-processing, were a smaller medial metal nanoparticle size(<6 nm), a lower metal-acid site ratio, as well as presencein the catalyst of fcc FeNi alloy structure and fcc Ni doped withFe.

One-pot synthesis of menthol from citronellal or citral was summarized. Both batch and continuous reactors have been recently applied. This reaction is very complex and a bifunctional catalyst exhibiting especially Lewis acid sites for cyclisation of citronellal to isopulegol are needed, while metal particles are required for its hydrogenation to menthols. Typically, too mild acidity of the catalyst and small particles do not catalyze menthol formation. Furthermore, too high acidity causes catalyst deactivation and dehydration of menthol. Very high menthol yields have been obtained in batch reactor over nobel and transition metal supported bifunctional catalysts. Shape selectivity was demonstrated for Ni-supported on Zr-modified beta zeolite, which gave high diastereoselectivity to the desired L-menthol. Recently one-pot synthesis of menthol in a trickle bed reactor has been investigated. Catalyst suffers only minor deactivation in transformation of citronellal to menthol, while more severe catalyst deactivation occurred in transforming citral to menthols. Noteworthy from the industrial point of view is that the product distribution obtained with the same catalyst under kinetic regime or under diffusional limitations differs from each other. The metal location and synthesis method of extrudates can have a major effect on the catalyst performance. Kinetic modelling of the data obtained from the trickle bed reactor considering the effectiveness factor is discussed. Graphical Abstract The results from one-pot synthesis of menthol finding applications in pharmaceuticals and fragrances from citral and its hydrogenated product, citronellal over bifunctional catalysts metal–acid are summarized. The relationship between the catalyst properties and the performance is discussed. In the continuous mode catalyst deactivation becomes apparent and in such mode of operation the product distribution might differ from those obtained in a batch reactor.

The current work focuses on studying the aqueous phase reforming (APR) of pine and birch hydrolysate obtained from waste wood by using organic acids available from biorefineries. Processing of representative synthetic mixtures was utilized in the work in order to support data interpretation related to the influence of different chemical compound and processing parameters on the APR of the actual hydrolysates. It was shown, that hydrogenation of the hydrolysates prior to APR was not feasible in the presence of formic acid, which ruled out one potential processing route. However, it was successfully demonstrated that birch and pine hydrolysates could be directly processed obtaining close to full conversion. The best results were obtained with tailored bimetallic Pd-Pt/sibunit catalyst in a trickle bed reactor system in the temperature range 175 degrees C-225 degrees C.

Citronellal cyclization was carried out in a continuous mode over H-beta-25 zeolite-based extrudates in a trickle-bed reactor at 35 °C and 10 bar of Ar. The physicochemical properties of zeolitic catalysts in the form of extrudates with a different diameter (1.4–3 mm) containing 30 wt % of a binder were correlated with the catalytic results. Alumina, aluminosilicate clay, and colloidal silica were used as binders. For extrudates with 1.4 mm in diameter, a significant decrease in the surface area, pore volume, and the total number of acid sites was observed in comparison to the values expected from a simple mechanical mixture of constituents. The specific surface area was similar, while the pore volume and mechanical strength decreased with increasing extrudate diameter. For all catalysts, conversion of citronellal and the yield of the desired pulegols decreased because of lower acidity and more prominent mass transfer with a size increase, while the selectivity ratio for different pulegols was similar. Overall, the effect of mass transfer on catalytic results in citronellal cyclization was larger than the effect of acidity. The yield of pulegols and the ratio of isopulegol ethers were correlated with strong Brønsted and strong Lewis acid sites, respectively. A proper selection of the binder and diameter of the extrudates plays a crucial role in the cyclization of citronellal.

Formic acid is one of the key components in green chemistry being involved in energy storage, production of chemical intermediates and fuel components. Therefore the knowledge of its stability is of crucial importance and a systematic study of its decomposition is needed. The kinetics of formic acid decomposition to hydrogen and carbon dioxide was investigated in a laboratory-scale fixed bed reactor at 150-225 degrees C and atmospheric pressure. Palladium nanoparticles deposited on porous active carbon Sibunit were used as the heterogeneous catalyst. The catalyst was characterized by nitrogen physisorption and high-resolution transmission electron microscopy. The average palladium nanoparticle size was 5-6 nm. The impacts of mass transfer resistance and formic acid dimerization were negligible under the reaction conditions. Prolonged experiments revealed that the catalyst had a good stability. Hydrogen and carbon dioxide were the absolutely dominant reaction products, whereas the amounts of carbon monoxide and water were negligible. The experimental data were described with three kinetic models: first order kinetics, two-step adsorption-reaction model and multistep adsorption-decomposition model of formic acid. The multistep model gave the best description of the data.

One-pot continuous synthesis of menthols both from citronellal and citral was investigated over 5 wt% Ni supported on H-Beta-38-sepiolite composite catalyst at 60-70 degrees C under 10-29 bar hydrogen pressure. A rela-tively high menthols yield of 53% and 49% and stereoselectivity to menthol of 71-76% and 72-74% were obtained from citronellal and citral respectively at the contact time 4.2 min, 70 degrees C and 20 bar. Citral conversion noticeably decreased with time-on-stream under 10 and 15 bar of hydrogen pressure accompanied by accu-mulation of citronellal, the primary hydrogenation product of citral, practically not affecting selectivity to menthol. A substantial amount of defuctionalization products observed during citral conversion, especially at the beginning of the reaction (ca. 1 h), indicated that all intermediates could contribute to formation of menthanes. Ni/H-Beta-38-sepiolite composite material prepared by extrusion was characterized by TEM, SEM, XPS, XRD, ICP-OES, N-2 physisorption and FTIR techniques to perceive the interrelation between the physico-chemical and catalytic properties.

One-pot continuous synthesis of menthols from citral was performed over 5 wt % Ni supported on a mesoporous aluminosilicate catalyst with sepiolite as a binder at 70 °C with a selectivity of 75% to menthols. Catalyst deactivation with time-on-stream resulted in a decrease of the conversion and selectivity to menthols at the expense of higher selectivity to isopulegols. Stereoselectivity to isopulegols and menthols only slightly changed with conversion and TOS. A kinetic model capable of describing experimental data for transformations of citral to menthol in a continuous mode was developed. It was based on a detailed reaction network and also comprised deactivation on both metal and acid sites. Numerical data fitting confirmed a good correspondence between the experimental data and calculations.

The current review critically summarizes recent developments in transformations of syngas to higher alcohols. Although higher alcohols have found applications as fuel additives, detergents and plastics for a long while, transformation of alcohols to jet fuel has attained recent interest due to an urgent need to develop jet fuels from sustainable sources. Fermentation of lignocellulosic-based sugars to ethanol as a technology does not compete with the food chain supply being thus a potentially acceptable route if economically viable. An alternative method is to gasify biomass to produce syngas, which can further be transformed to higher alcohols through several pathways. Jet fuel range alkanes are obtained from alcohols via oligomerisation, dehydration and hydrogenation. The highest space time yields of higher alcohols of 0.61 g/(g(cat)h) is obtained over a bimetallic copper-iron catalyst supported on a hierarchical zeolite at 300 degrees C and 5 MPa. Furthermore, copper-cobalt and cobalt-manganese compositions are promising for the direct synthesis of higher alcohols from syngas, where one of the challenges is to suppress formation of alkanes and CO2 and increase selectivity to higher alcohols. From the mechanistic point of view, it has been proposed to use dual-site catalysts, where one site promotes hydrogenation, while the other site is required for the chain growth. In addition to selection of the optimum reaction conditions and catalyst properties, kinetic modelling, thermodynamics and scale up issues are discussed.