Slurry Reactor Research Articles

Reaction of Carbon Dioxide Gas Absorption with Suspension of Calcium Hydroxide in Slurry Reactor

Chemical phenomena involving three phases (solid, liquid, and gas) are often found in the industry. Carbonate (CaCO3) is widely used in industries as a powder-making material in the cosmetic industry, a pigment in the paint industry, and filler in the paper and rubber industry. This research aim to study the ordering process carbonate deposits (CaCO3) from the absorption process of CO2 gas with Ca(OH)2 suspension. The absorption reaction of CO2 gas with Ca(OH)2 suspension was carried out in a stirred slurry tank reactor. Initially, the reactor containing water was heated to a certain temperature, then Ca(OH)2 was added to the reactor. Furthermore, CO2 gas with a certain flow rate and temperature (according to the reactor temperature) is flown with the help of a gas distributor. Samples were taken every 1 min until the concentration of Ca(OH)2 could not be detected (completely reacted). The variables in this study were: stirrer rotation speed (5.66711.067 rps), CO2 gas flow rate (34.0127–60.5503 c/s), and temperature (30–50°C). The mass transfer coefficient and the reaction rate coefficient were determined by minimizing Sum of Squares of Errors (SSE). This experimental process follows a dynamic regime. A dimensionless number relationship for the gas-liquid mass transfer for the value range is Re1 = 18928.76-38217.20, Sh = 0.07928 Reg0.4383 Rel0.4399 Sc0.6415 with an error of 5.19%. The dimensionless number relationship for solid-liquid mass transfer is Sh = 0.0001179 Reg0.4674 Rel0.5403 Sc1.444 with an error of 7.31%. The relationship between the reaction rate constant and the temperature in the 30-50 °C range can be approximated by the Arrhenius equation, namely kr = 1771000 e-2321.4/T cm3/mgmol/s with an error of 3.63%. Doi: 10.28991/ESJ-2023-07-02-02 Full Text: PDF

Reverse water gas shift reaction over a Cu/ZnO catalyst supported on regenerated spent bleaching earth (RSBE) in a slurry reactor: the effect of the Cu/Zn ratio on the catalytic activity.

The catalytic conversion of CO2 via the Reverse Water Gas Shift (RWGS) reaction for CO production is a promising environment-friendly approach. The greenhouse gas emissions from burning fossil fuels can be used to produce valuable fuels or chemicals through CO2 hydrogenation. Therefore, this project was to study the CO2 conversion via RWGS over various Cu/ZnO catalysts supported by regenerated spent bleaching earth (RSBE) prepared by wet impregnation technique with different Cu : Zn ratios (0.5, 1.0, 1.5, 2.0, 3.0). The causes of environmental pollution from the disposal of spent bleaching earth (SBE) from an edible oil refinery can be eliminated by using it as catalyst support after the regeneration process. The synthesized catalysts were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), temperature-programmed reduction of hydrogen (TPR-H2), pyridine-adsorbed Fourier transform infrared (FTIR-pyridine), temperature programmed desorption of carbon dioxide (TPD-CO2), N2 physisorption, and Fourier transform infrared (FTIR) analysis. The RWGS reaction was carried out in a slurry reactor at 200 °C, with a pressure of 3 MPa, a residence time of 4 h, and catalyst loading of 1.0 g with an H2/CO2 ratio of 3. According to experimental data, the Cu/Zn ratio significantly impacts the catalytic structure and performance. The catalytic activity increased until the Cu : Zn ratio reached the maximum value of 1.5, while a further increase in Cu/Zn ratio inhibited the catalytic performance. The CZR3 catalyst (Cu/Zn ratio of 1.5) with a higher catalytic reducibility, high copper dispersion with small crystalline size, lower total pore volume as well as higher basicity showed superior catalytic performance in terms of CO2 conversion (40.67%) and CO yield (39.91%). Findings on the effect of reaction conditions revealed that higher temperature (>240 °C), higher pressure (>3 MPa), higher reaction time (>4 h) and higher catalyst loading (>1.25 g) could improve CO2 conversion to CO yield. A maximum CO2 conversion of 45.8% and multiple recycling stability of the catalyst were achieved, showing no significant decrease in CO2 conversion.

Combustion induced synthesis of multicomponent Cu-based catalysts for autocatalytic CO hydrogenation to methanol in a three-phase reactor system

The MgO and ZnO in the CuZnOMgO catalytic system in a slurry reactor result in improved activity and stability, respectively. The slurry reactors induce the autocatalytic methanol synthesis which results in a higher space–time yield.

ANALYSIS OF CATALYTIC BEHAVIOR OF RHENIUM PROMOTED PT/TIO2 CATALYST IN ERYTHRITOL HYDROGENOLYSIS

Rhenium modified Pt/TiO2 catalyst has been tested during erythritol (ERY) hydrogenolysis reaction in a slurry reactor. N2 physisorption, temperature programmed reduction and CO chemisorption characterizations were performed. After reduction treatment, Pt species were fully reduced with a dispersion of 26% whereas Re species remained partially oxidized. ERY may convert through four pathways: isomerization, dehydration and C-O or C-C hydrogenolysis. Pt-Re/TiO2 was active and selective to butanetriols and butanediols formation. The influence of temperature (423–498 K) and reactant concentrations (15-35 barH2 and 0.2-0.6 MERY) on catalytic activity and products distribution were evaluated; the activation energy and the reaction orders for each route were estimated. Dehydration pathway displayed the highest activation energy whereas isomerization showed the lowest value. The order to ERY and H2 were 0.23 and 0.97 respectively, for C-O hydrogenolysis route and is consistent with two different mechanisms proposed for the removal of primary or secondary OH group.

Experimental mass and heat transfer at a serpentine tube heat exchanger located at the wall of a square stirred tank reactor

• Rates of mass and heat transfer of a serpentine tube heat exchanger were studied. • The serpentine is located at the wall of a square stirred tank reactor. • Variables studied were impeller speed and geometry, tube diameter, and tube pitch. • Dimensionless correlations were developed to design and operate the heat exchanger. • The possibility of using the serpentine tube as a catalyst support was highlighted. Although the study of the heat transfer behavior of stirred tank heat exchangers such as helical coils, vertical tube baffles, and cooling jackets has received much attention, no study has been reported on the heat or mass transfer behavior of serpentine tube heat exchangers, so the present work aims to study rates of mass and heat transfer (by analogy) at the outer surface of a serpentine tube heat exchanger located at the wall of a square stirred tank reactor by the electrochemical technique. Variables studied were impeller rotational speed, impeller geometry, tube diameter, and tube pitch. The mass or heat transfer coefficients were found to increase with increasing impeller speed and decrease with increasing cylinder diameter and pitch. For a given set of conditions, a radial flow turbine produces higher rates of mass transfer than an axial flow turbine. The data were correlated by dimensionless mass transfer correlations which can be used to scale up and operate the heat exchanger. When the mass transfer data at the serpentine tube were compared with those at an active flat wall of equal height, it was found that the mass transfer rate at the serpentine tube is higher than that of the flat wall by an amount ranging from 10% to 210% depending on the operating conditions. The possibility of using the serpentine tube as a catalyst support for conducting diffusion-controlled exothermic immobilized cell biochemical reactions which need rapid cooling to avoid thermal degradation of the biomass was highlighted. The dual-use of the serpentine tubes as a catalyst support and a cooler would reduce the capital and operating costs of immobilized enzyme or cell stirred tank biochemical reactors compared, for instance, with the traditional stirred slurry reactor owing to the elimination of the costly and time-consuming process of separating the final product from the catalyst particles.

Liquefaction, cracking and hydrogenation of microalgae biomass resources to CO2 negative advanced biofuels: Mechanisms, reaction microkinetics and modelling

Deoxygenation of triglycerides is one of the crucial pathways for the production of oxygen-free hydrocarbons and biofuels that are fully compatible with conventional internal combustion engines. The one-step liquefaction and hydrotreatment of Chlorella sorokiniana microalgae was investigated in a three-phase slurry reactor. The production of diesel-like hydrocarbons was successfully accomplished over sulfide form of NiMo/Al2O3 catalyst under hydrogen atmosphere. The present work contains a comprehensive investigation of the temperature and hydrogen pressure influence on the final product composition. The highest yield of C18 and C16 (26.1% and 10.7%, respectively) was reached by increasing the reaction temperature to 350 °C and hydrogen pressure to 50 bar, while at milder conditions (200 °C and 20 bar) the products appeared only in trace concentrations. In order to obtain an accurate kinetic model, reaction mechanism was first needed to be determined based on experimentally obtained products and intermediates. A simplified reaction pathway contains liquefaction, hydrogenolysis, hydrodeoxygenation, decarboxylation and decarbonylation. The model comprises mass transfer phenomena involved in the liquefaction process, the mass transfer of hydrogen from gas to liquid phase, adsorption, desorption and surface reaction kinetics. The lowest rate constant was calculated for the microalgae conversion to triglycerides (k0 = 1.93 × 10−6 min−1), indicating slow liquefaction.

Modelling and validation of energy systems with dynamically operated Power to Gas plants for gas-based sector coupling in de-central energy hubs

Participants of the COP 26 summit have agreed to limit global temperature rise to 1.5 K by 2050. Out of the many strategies envisaged to meet the targets of COP 26, the ‘Sector Coupling’ process aims to use renewable electricity in residential heating, chemical industry, and transportation sectors. Several studies predict that de-central energy systems will play a significant role in the future. Among the proposed sector coupling strategies in de-central energy systems, the Power to Gas (PtG) process producing chemical energy carriers like Substitute Natural Gas (SNG) from renewable power is gaining acceptance. Numerical models of de-central energy systems are needed to analyse sector coupling under fluctuating renewable energy generation and changing gas demand. This study introduces a numerical model of a decentral energy system that includes a novel methanation concept developed at the Engler Bunte Institut of KIT called 3 Phase Methanation. Here, H2 from electrolysis and CO2 from DAC or other biomass-based sources are passed through a slurry bubble column reactor. The slurry is a suspension of the catalyst in a liquid heat transfer medium where the heat of the reaction is dissipated. The 3-Phase methanation process is modelled in this study using the axial dispersion method. Earlier studies describing experimental campaigns conducted on the pilot plant in KIT have proven that the reactor core is nearly isothermal with stable product gas compositions even if the load changes are instantaneous. In this study, it is shown that the numerical model can replicate the experimental results. Following modelling and validation, the numerical model of the PtG plant is integrated with the other components to simulate the de-central energy system. The simulation results demonstrate the dynamic output of all the components and, in particular, the response provided by the PtG plant. This model can be adapted to simulate sector coupling in future de-central energy systems and analyse aspects like long-term energy storage, GHG minimisation and cost-optimal operation.

A Thermodynamic Simulation Package for Catalytic Polyolefin Reactors: Development and Applications

AbstractA thermodynamic simulation package is developed for the catalytic polymerization of olefins in autoclave slurry, loop slurry, gas‐phase, and autoclave solution reactors. The number of components in the reactors may vary from two to six. The simulator uses the Sanchez–Lacombe theory, one of the major thermodynamic models in the polymer industry. Step‐by‐step instructions on how to specify the system, derive and solve the resulting nonlinear equations, and estimate the required thermodynamic properties are given. The software is used to describe ethylene/1‐hexene copolymerizations with hydrogen in different reactors under industrial conditions. These simulations demonstrate why thermodynamic effects must be included in olefin polymerization models.

An optofluidic planar microreactor with photoactive Cu2O/Mo2C/TiO2 heterostructures for enhanced visible light-driven CO2 conversion to methanol

Mixing TiO2 with Mo2C has recently been proposed to improve the photocatalytic conversion of CO2 to methanol under visible light irradiation, although further efforts are still needed to enhance process performance. In this context, the use of p-type semiconductors (i.e., Cu2O) in co-doping strategies can enhance not only the redistribution of electric charges due to its narrowing bandgap, but also the selectivity of the reaction towards methanol. This work focuses on the development of a continuous visible light-driven CO2 photoconversion to methanol process in an optofluidic microreactor using Cu2O/Mo2C/TiO2 heterostructures. A significant improvement in process performance can be seen under visible light with the heterostructures containing 4 wt% of Cu2O. Superior methanol production rates (36.3 µmol∙g−1∙h−1) with an apparent quantum yield = 0.64% and a reaction selectivity = 0.93 are reached, in comparison with the results achieved at Cu2O-free Mo2C/TiO2 photocatalytic surfaces (11.8 µmol∙g−1∙h−1, 0.21% and 0.92, respectively). This can be adscribed to the role of Cu2O in the selectivity of the reaction towards methanol. The synergetic effect between Cu2O, Mo2C, and TiO2 in the heterostructures may also provoke a more efficient charge separation and transfer, while enhancing the visible light absorption properties of the material and its photocatalytic stability. The maximum methanol rate outperforms most of the values previously reported in slurry batch reactors and evidences the possibility of enhancing the continuous visible light-driven CO2-to-methanol photoconversion process with efficient metal co-doping approaches in optofluidic microreactors.

Effect of copper source on the structure–activity of CuAl2O4 spinel catalysts for CO hydrogenation

Due to the complexity of the structure–activity relationship of the CuAl2O4 spinel catalyst, optimization of the catalyst structure is a great challenge. In this paper, three different CuAl2O4 spinel catalysts were prepared by the solid-phase method using copper hydroxide, copper nitrate, and copper oxide as the copper source, respectively, to study the difference in the structure of CuAl2O4 spinel catalysts induced by the raw materials and the catalytic behavior for CO hydrogenation. The structure of CuAl2O4 spinel catalyst was characterized by XRD, BET, SEM, TEM, H2-TPR and XPS. The activity of CO hydrogenation over the CuAl2O4 spinel catalyst without pre-reduction was evaluated in the slurry reactor. The results demonstrated that different copper sources had obvious influence on the CuAl2O4 spinel texture properties, surface enrichment degree, as well as decomposition and reduction ability, which further regulated the ratio of Cu+/Cu0 and thus affected the catalytic performance, especially the alcohol distribution. The CuAl2O4 spinel, employing copper hydroxide as the copper source, showed better selectivity of C2+OH, which was assigned to a higher ratio of Cu+/Cu0, along with larger pore size and pore volume. Moreover, the synergistic effect between Cu0 and γ-Al2O3 improved the selectivity of dimethyl ether.

Plastic waste upgrade to olefins via mild slurry microwave pyrolysis over solid acids

Chemical upcycling technologies are emerging as the most viable to combat plastic waste accumulation. Among them, catalytic pyrolysis is very promising as it is feedstock agnostic. However, the high energy demand associated with pyrolysis can lead to significant carbon dioxide production. Here, we demonstrate that coupling microwave heating with suitable solid acid promoters in a slurry reactor coupled with a distillation unit can overcome the energy-related challenge of conventional pyrolysis, by operating at modest temperatures (350–375 °C), enhancing transport, and furnishing high yields of olefins (∼88 %) in seconds, with medium-sized olefins (>75 %) composing a significant fraction. Reduced thermal gradients minimize coke formation, further improving the performance. Techno-economic analysis and life cycle assessment indicate the potential of the technology.

Vegetable Oil Hydrogenation over Pt Monolithic and Powder Catalysts: Experimental and Modeling Study

AbstractA complete kinetic study was performed for the hydrogenation of vegetable oil using a powder and a monolithic Pt catalyst. The experimental studies were carried out at a wide interval of H2 pressure, temperature, and catalyst loading using Pt/γ‐Al2O3 powder catalyst in a slurry reactor and Pt/Al2O3/Al‐structured catalyst in a monolithic stirrer reactor. The mathematical model for the reactors includes the hydrogenation and isomerization reactions, the external gas‐liquid and liquid‐solid mass transfer as well as the internal mass transfer. Four kinetic models were evaluated for both catalysts. The best fit of the experimental data was obtained by adopting a Langmuir‐Hinshelwood kinetic model for the liquid reactant and a dissociative adsorption and zero‐order reaction for H2.

Experimental and theoretical study unveiling the role of solvents on CO activation and hydrogenation to methanol in three-phase reactor system

Syngas conversion to methanol in the slurry reactor is a developing technology where selecting suitable solvent is a crucial step. The activity test were performed in the stirred tank slurry reactor at 240 °C, 50 bar, 1000 rpm with three different solvents (paraffin, diglyme and DMSO) with CuZnO (CuO:ZnO = 40:60 by weight) catalyst to solely study the role of solvents. In the presence of the diglyme more CO conversion and methanol selectivity was obtained than paraffin and DMSO. Further, the CO adsorption on Cu(111) is calculated by DFT combined with the Conductor like Screening Model (COSMO) model to study the solvent effect. CO activation and stability have been studied by analyzing surface energy, adsorption energy, Mulliken charges of CO and Cu (111), Partial density of states (PDOS), sigma profiles, and dipole moment of the free CO in solvents. PDOS peaks of free CO shifted towards Fermi level in the presence of solvents which highlights the role of solvents in CO adsorption on Cu(111). Sigma profiles uncover facile CO adsorption on the hollow sites of Cu (111) facet in the presence of the solvent. Surface energy of the Cu(111) in different solvents are calculated which signifies the more surface area exposure in the presence of diglyme. The experimental results validated by the theoretical results revealing the role of moderate polarity in CO hydrogenation. This work will provide insight on the potential solvent selection for the methanol synthesis in a slurry reactor.

Green synthesis approach for preparing zeolite based Co-Cu bimetallic catalysts for low temperature CO2 hydrogenation to methanol

In this study, zeolite based Cu-Co bimetallic catalysts were synthesized by green deposition precipitation method. To investigate the optimum metal-metal ratio, catalysts with different Cu-Co metal weight ratios were evaluated for CO2 hydrogenation to methanol. The XRD analysis revealed crystalline nature of zeolite support with deposition of highly dispersed Cu-Co metal oxides. The FESEM observation showed well dispersed morphology of zeolite based Cu-Co bimetallic catalysts. The nitrogen adsorption-desorption studies showed that surface area of Cu-Co bimetallic catalysts was slightly decreased by increasing Cu content in bimetallic catalysts. Temperature program reduction studies exhibited synergism between the Cu-Co metals which resulted variation in reduction behavior of zeolite based Cu-Co bimetallic catalysts. Similarly, XPS studies revealed metal-metal interaction by shifting XPS peaks to higher binding energies regions. Temperature program desorption investigations showed the existence of three types of basic sites on the surface of zeolite based Cu-Co bimetallic catalysts. Activity profiles of zeolite based Cu-Co bimetallic catalysts were examined for low temperature CO2 hydrogenation to methanol in slurry reactor. The activity studies documented enhancement in methanol synthesis rate from 7.5 to 25.6 g/Kgcat.h by increasing the Cu content in catalysts. Based on the physico-chemicals findings and activity data, structure-activity patterns were elaborated in details.

Upgrade of a slurry photocatalytic membrane reactor based on a vertical filter and an external membrane and testing in the photodegradation of a model pollutant in water

Submerged slurry photocatalytic membrane reactors have been widely investigated in literature to combine photocatalysis and membrane separation in the mineralization of recalcitrant pollutants in wastewaters. However, submerged membranes are only able to retain the photocatalyst particles and not many types of pollutants. An upgraded configuration, based on a vertical filter (able to retain the photocatalyst) and an external nanofiltration (NF) membrane (able to retain pollutants in the photoreaction zone), has been designed, built and tested. To our knowledge, this novel configuration has never been proposed. The proof-of-concept on the working and behavior of the vertical filter in presence of the photocatalyst and the photocatalytic performance of the overall system, in a batch configuration, in the photodegradation of gemfibrozil as a model pollutant are reported. The filter was able to retain the TiO2 particles while ensuring greater flux compared to a submerged membrane (200 vs 40 L m-2 h-1 average values). The external membrane is not exposed to light irradiation, permits the recycle in the photoreactor of the non-photodegraded pollutants and produce a quality of the treated water (permeate) better than a submerged membrane. Some parameters (e.g.: TiO2 amount, pH, light intensity and wavelength, air and oxygen, membrane rejection) that influence the performance of this integrated system (photoreactor, filter and membrane) have been studied and discussed. Indeed, a pH 8.0 (giving 40–50 % rejection of the Fortilife NF membrane) was chosen against pH 9.7 (giving 90 % rejection), to avoid filter plugging. The obtained overall performance (80 % reduction of gemfibrozil concentration) can be further improved by a fine tuning of the various parameters.

Formic acid-to-hydrogen on Pd/AC catalysts: Kinetic study with catalytic deactivation

A kinetic model for formic acid (FA) decomposition over a commercial 10 wt% Pd/AC catalyst has been developed to describe the hydrogen production and to understand the deactivation mechanism. The kinetic data were obtained in a batch slurry reactor in absence of mass transfer limitation at: CFA,0 = 0.25–2 M, CCAT = 1 g L−1, T = 25–85 ºC and P = 1 atm. The catalyst stability was studied in successive cycles at different temperatures. Fresh, used and regenerated Pd/AC catalysts were deeply characterized to gain insight into the activity, selectivity and stability. H2 and CO2 were the only reaction products detected. The reaction follows a first order kinetic for FA while the activity shows exponential decay with the initial FA concentration and reaction temperature. This paper represents a step forward in the on-site hydrogen production technology by using FA as liquid organic hydrogen carrier.

Sugar acid production on gold nanoparticles in slurry reactor: Kinetics, solubility and modelling

Sugar acids obtained by oxidation of sugars are very valuable molecules which are used as chelating agents, binders as well as ingredients in pharmaceuticals. Arabinonic acid was prepared by oxidation of arabinose on gold nanoparticles deposited on an aluminium oxide carrier. A systematic reaction kinetic study was conducted to reveal the influence of oxygen partial pressure and pH on reaction rate and product selectivity. Experiments were carried out in a laboratory-scale semi-batch reactor which was operated at 70 °C and oxygen partial pressures 0.125–1.0 atm. The pH of the aqueous sugar solution was 6–8. Oxygen was continuously flowing through the semibatch slurry reactor and the pH was kept constant by adding NaOH during the experiments. The oxygen solubility in the reaction mixture was determined in separate experiments. A reaction mechanism was proposed for the formation of arabinonic acid (main product) and arabinolactone (intermediate by-product). The surface reaction of competitively adsorbed arabinose and oxygen was assumed to be rate determining for the arabinose consumption. For the formation of arabinonic acid from arabinolactone, the rate determining step was presumed to be the reaction between arabinolactone and sodium hydroxide. The reactor was described with the perfect backmixing model and the component mass balances were solved numerically during the estimation of kinetic parameters by nonlinear regression analysis. The kinetic model gives new insights in the reaction mechanism and described the experimental data very well. The model has potential for application in the oxidation of other monomeric sugars, too.

Interaction forces and suspension characteristics in an oscillatory membrane photocatalytic reactor

The effects of the interaction between the hydrodynamic and colloidal forces on the suspension and performance characteristics of a slurry photocatalytic reactor equipped with oscillatory membrane and lateral turbulence promoters are investigated. Aggregation of catalyst particles is influenced by the magnitude of colloidal forces between the particles in relation to the hydrodynamic stresses acting on the aggregate. The interaction of the axial oscillatory shear with the transverse motion of the turbulence promoters (TP) results in generation of vortices and eddies that extended further away from the membrane surface leading to reducing particle aggregation. For the range of oscillatory conditions investigated, the aggregate size remained in the viscous subrange and decreased with increasing the oscillation intensity where an almost three folds decrease in aggregate size was achieved at high oscillation intensities. This resulted in reducing particles settling and deposition on the membrane surface which increased the catalyst specific area and volume fraction in suspension and enhanced both membrane flux and reaction rates. Improvement of the latter is also achieved by the microscale eddies attenuation of the concentration boundary layer surrounding the catalyst particles which results in better mass transfer. Using methylene blue dye (MB) degradation with ZnO photocatalyst under UV illumination as a model photocatalytic reaction, the investigation showed that increasing the oscillation intensity resulted in higher membrane flux and reaction rates that asymptotically approached maximum corresponding to near maximum catalyst suspension. This was estimated based on the magnitude of the eddy forces in the suspension in relation to the sedimentation and permeate drag forces acting on the catalyst particles. Comparison between the results of the present investigation and data from the literature showed satisfactory agreement.

Abatement of Naphthalene by Persulfate Activated by Goethite and Visible LED Light at Neutral pH: Effect of Common Ions and Organic Matter

Naphthalene (NAP) has received particular attention due to its impact on the environment and human health, mandating its removal from water systems. In this work, the abatement of NAP in the aqueous phase was achieved using persulfate (PS) activated by Fe (III) and monochromatic LED light at a natural pH. The reaction was carried out in a slurry batch reactor using goethite as the Fe (III) source. The influence of the PS concentration, goethite concentration, irradiance, temperature and presence of organic matter, chloride, and bicarbonate on the abatement of NAP was studied. These variables were shown to have a different effect on NAP removal. The irradiance showed a maximum at 0.18 W·cm−2 where the photonic efficiency was the highest. As for the concentration of goethite and PS, the influence of the first one was negligible, whereas for PS, the best results were reached at 1.2 mM due to a self-inhibitory effect at higher concentrations. The temperature effect was also negative in the PS consumption. Regarding the effect of ions, chloride had no influence on NAP conversion but carbonates and humic acids were affected. Lastly, this treatment to remove NAP has proved to be an effective technique since minimum conversions of 0.92 at 180 min of reaction time were reached. Additionally, the toxicity of the final samples was decreased.

Low temperature green methanol synthesis by CO2 hydrogenation over Pd/SiO2 catalysts in slurry reactor

The utilization of the greenhouse gas of carbon dioxide (CO2) for fuel and value-added chemicals synthesis has become globally indispensable process for healthy environment. In this context, the hydrogenation of CO2 to methanol is an attractive avenue for achieving such goal. Thus, we prepared mesoporous silica-supported nanocrystalline palladium metal (Pd) for methanol synthesis by CO2 hydrogenation. To investigate the role of Pd metal, the synthesized mesoporous silica was loaded with 1, 2, 3 and 4 wt% of Pd. Physicochemical profile of synthesized mesoporous silica supported Pd catalysts were assessed by Inductively coupled plasma - optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), Field-Emission Scanning Electron Microscopy (FESEM), Nitrogen adsorption–desorption and Temperature Program Reduction (TPR) techniques. ICP-OES measurement confirmed the actual Pd metal loading on the mesoporous silica support. XRD confirmed amorphous and crystalline nature of mesoporous silica and Pd metal, respectively. FESEM images exhibited homogenous and well dispersed Pd metal particles on the surface of mesoporuse silica support. Nitrogen adsorption desorption studies displayed enlargement in BET surface area with Pd promotion. Reduction behaviour of PdO was revealed by TPR data over the studied temperature range. The structure–activity studies suggested the degree of Pd crystallinity and higher dispersions as amongst the main factors contributing to the performance of Pd/SiO2 catalysts for pure CO2 hydrogenation in slurry reactor.