By-product CO Research Articles

CO2 hydrogenation to light olefins over highly active and selective Ga-Zr/SAPO-34 bifunctional catalyst

The production of light olefins from the hydrogenation of CO2 is an efficient way to utilize CO2, where the surface oxygen vacancy in metal oxide plays an important role in CO2 adsorption and activation. Here, the Ga-Zr metal oxides were prepared by hydrolysis of urea at different temperatures and combined with SAPO-34 to prepare the bifunctional catalyst for CO2 hydrogenation to light olefins. The surface oxygen vacancy content of Ga-Zr oxide increases with increasing urea hydrolysis temperature, and a high CO2 conversion of 26.4% and C2=–C4= hydrocarbon selectivity of 87.2% were obtained by a well-matched amount of desorbed CO2 and H2. Using the CO2 and H2/HCOOH/CH3OH as probe molecules, the in-situ DRIFT spectra reveal that the CO2 could be activated on surface oxygen vacancy and converted to CO3* and HCO3* species, which were further hydrogenated to HCOO* and CH3O* species. While the by-product CO mainly originates from the decomposition of HCOO* and the presence of SAPO-34 converts CH3O* to C2=–C4=. The current study illustrates that boosting the surface oxygen vacancy in defected surfaces of metal oxide and providing a matching H2 dissociation ability is the key to improve the performance of CO2 hydrogenation to light olefins.

NiO/vermiculite composites prepared for photocatalytic degradation of methanol-water solution and hydrogen generation

A novel eco-friendly NiO/Vm clay based photocatalysts were synthesized from two vermiculites (Vm1 and Vm2) and nickel(II) nitrate hexahydrate (Ni(NO3)2·6H2O salt precursor by the chemical precipitation without and with the sodium hydroxide (NaOH) or ammonium hydroxide (NH4OH, 28% NH3 in H2O) as precipitation agents (Synthesis A) in comparison with the solid-state thermal decomposition (Synthesis B) at 600 °C. Structural properties of all specimens were characterized by X-ray fluorescence, scanning electron microscopy, X-ray diffraction, infrared (IR) and Raman spectroscopy. The photocatalytic performance of NiO/Vm composites was evaluated under UV radiation (λ = 254 nm) for decomposition of methanol-water to hydrogen over 4-h and the stable yield of hydrogen over the 24-h periods. The NaOH and NH4OH affected the NiO crystallite size and therefore the photocatalytic activity during 4 h. Different 2:1 layer charge of Vm1 (0.82 e−) and Vm2 (0.40 e−) and the specific surface area of Vm1 (about 43 m2/g) and Vm2 (about 34 m2/g) supported H2 yield of 628.2 μmol/gcat. and 596.8 μmol/gcat., close to 657.0 μmol/gcat. produced in the presence of commercial photocatalyst TiO2 Evonik P25. Crystalline NiO precipitated and anchored in NiO/Vm composites contained smaller crystallites than those in free NiO. Vermiculite silica surface supports coverage of NiO by hydrogen bonding to Si-OH groups influencing the geometry of the NiO crystal structure (disorder NiO(X)). The heterojunction with Si-O-Ni bonding, at which electrons transfer from Vm to NiO cause enriching electron density in NiO and favoring its photocatalytic activity. Photocatalytic hydrogen generation from methanol–water mixture at the presence of all specimens indicated the main product H2 and minimum by-products CH4 and CO. The stable hydrogen production for 24 h was confirmed only in the presence NiO/Vm1–24 while maintaining the NiO(X) in small crystallites. The thermal solid-state procedure provided the gradual dehydration of vermiculites and Ni(NO3)2·6H2O to the same amount and crystallinity of NiO in NiO/Vm1 and NiO/Vm2 composites. The results of this work confirm that vermiculites mixed layer structures with different negative layer charge play a dominant role as semiconductors for anchored NiO. The photocatalytic activity of NiO/vermiculite composites can be harnessed to treat wastewater containing organic contaminants.

Realizing synergy between Cu, Ga, and Zr for selective CO2 hydrogenation to methanol

Hydrogenating CO2 to methanol with high yields and selectivity remains a kinetic challenge. We report ternary Cu-Ga-Zr catalysts with promising performances. Methanol productivity and selectivity were highest on coprecipitated samples containing approximately 20 wt% of each metal. At 7% isoconversion, this ternary system was more selective to methanol (60 ± 1%) than CuZrOx (51 ± 1%) and CuGaOx (53 ± 3%) at the same Cu loading. We uncover the importance of the Cu/Zr interface for CO2 adsorption, Cu/Ga interface for H adsorption, and metallic Cu for H–H dissociation. Methanol formation on these catalysts was found to be first order in H2, implying the reaction was likely to be rate-limited by hydrogen activation. In fact, the methanol space-time yield correlated linearly with the H2/D2 exchange rate. We propose a catalytic pathway wherein the production of the byproduct CO is hindered by the presence of adsorbed H.

CO in situ directed highly efficient CrOx@silicalite-1 for propane oxidation dehydrogenation by CO2

The propane oxidation dehydrogenation assisted by CO2 (CO2-ODHP) is currently a hot research topic, not only to meet growing demand of propylene but also to favor the CO2 neutralization. In present work, a series of CrOx@S1-n-1.0 with different Cr contents (n= 2.2, 3.6 and 4.5 wt%) is synthesized based on a small gas molecule directing synthesis strategy, wherein the gaseous CO of 1.0 MPa was in situ introduced in the synthesis system to regulate the interaction and dispersion of CrOx over silicalite-1 (S1) support. The characterization results of XRD, XPS, H2-TPR, and Raman indicate that the CO can affect the oxidation state and dispersion of Cr species. As observed, the Cr species were highly dispersed over CrOx@S1–3.6 %-1.0 (in the form of Cr6+ valance state), which however would aggregate to generate Cr2O3 nanoparticles over the CrOx@S1–3.6 %-0a prepared by impregnation method in absence of CO. The activity measurement indicates that the CrOx@S1–3.6 %-1.0 possesses the highest activity by displaying an average propane conversion of 50.4 % and CO2 conversion of 23.6 % at 600 °C, which surpasses most of the literature reports. The CO2-ODHP reaction mechanism was further investigated by in situ DRIFTS, which indicates that dissociated H of propane can react with CO2 to form formate (-COOH), in turn further reacts with H to produce byproducts CO and H2O, and the formate species can also react with the CrO3 active site to form bicarbonate species (HCO-3). Generally, present work has proposed a small gas molecule directing strategy to adjust the dispersions and chemical states of the loaded guest meals over catalytic support. The study of present work would contribute to other highly efficient catalyst design.

Highly coupled MnO2/Mn5O8 Z-scheme heterojunction modified by Co3O4 co-catalyst: An efficient and stable photocatalyst to decompose gaseous benzene

MnOx Z-scheme heterojunction exhibits a strong redox capacity, thereby it has great potential in the field of photocatalysis for gaseous benzene oxidation to address environmental pollution. However, the self-oxidation of MnOx due to the accumulation of photogenerated holes severely restricts its practical application. Herein, a highly coupled MnO2/Mn5O8 Z-scheme heterojunction modified by Co3O4 co-catalyst grown on ammoniated carbon cloth (MnOx/Co3O4@ACC) was constructed through electrodeposition and applied for efficient photocatalytic benzene degradation. The optimized MnOx/Co3O4@ACC presents high-efficient degradability, mineralization rate and high stability after 60 cycles (30 h). Co3O4 served as a hole collector to promote the extraction of photogenerated holes from the MnOx surface, suppressing the photocorrosion of MnOx. Additionally, the by-product CO was more easily absorbed and activated on MnOx/Co3O4@ACC surface due to the introduction of Co3O4. The electrodeposition-photocatalysis strategy developed in this work shows great application prospects for environmental contaminant remediation.

The origin of the mediocre methanol selectivity of Cu/ZnO-based catalysts for methanol synthesis from CO2 hydrogenation

Cu/ZnO-based catalysts have been extensively and intensively studied for CO2 hydrogenation to methanol due to their relatively superior catalytic performance. However, the mediocre methanol selectivity over Cu/ZnO-based catalysts has not been disclosed mainly because the predominant by-product CO formation activity fails to arouse any attention, significantly deterring the further catalyst optimization. The ZnOx-Cu nanoparticles (NP)-ZnO interface, derived from strong metal-support interactions (SMSI), has been recognized to be more active for methanol formation compared with the classical direct contact Cu-ZnO interface. In order to disclose the origin of the mediocre methanol selectivity, these two types of Cu-ZnO interfaces have been designed and constructed through carefully manipulating the synthesis and heat pre-treatment conditions of the powder model catalysts. Then, methanol and CO formation behaviors over these two interfaces have been explored thoroughly in actual reaction conditions. Finally, the origin of the mediocre methanol selectivity over Cu/ZnO-based catalysts has been proposed. This work provides unique insights for designing efficient Cu/ZnO-based catalysts with high methanol selectivity and yield and puts forward an effective strategy to investigate the catalytic behaviors over different interfaces in actual reaction conditions.

CuO–ZnO catalyst decorated on porous CeO2-based nanosheets in-situ grown on cordierite for methanol steam reforming

Development of efficient and durable structured catalysts for hydrogen production by methanol steam reforming (MSR) is becoming extremely appealing owing to their low pressure drop and large open area. In this work, porous CeO2-based nanosheet array is in-situ grown on the surface of cordierite honeycomb ceramic by a simple hydrothermal approach. The generated porous nanosheet structure not only surpasses the obstacle of low specific surface area of cordierite (increasing from 4.4 to 252.6 m2 g-1), but also the peak area ratio of oxygen vacancies on the support surface rises from 19.7% to 29.7%, which are favorable to promote the catalytic activity and reduce by-product CO selectivity of structured catalysts in MSRreaction. Importantly, the structured catalysts formed by decorating CuO–ZnO catalysts on CeO2-based nanosheets via sol-gel combustion method remain porous structure, offering an ideal space for reactant entry and mass transfer diffusion, which facilitates reaction triggering and product discharge. The optimal structured catalyst achieves 100% methanol conversion at 260 °C without CO and the methanol conversion remains at 94.7% after 100 h of the reaction, exhibiting the excellent catalytic activity and durability. Thus, the structured catalyst has potential for industrial-scale preparation and application, especially for on-site hydrogen production in vehicles.

Enhanced catalytic activity for methanol synthesis from CO2 hydrogenation by doping indium into the step edge of Rh(211): A theoretical study

The doping of foreign metals can modify the electronic properties of the original catalyst surfaces, thereby changing the catalytic activity. Realistic surfaces possess many defects, such as step sites. Herein, the first-principles calculation is implemented to research how indium doping on stepped Rh(211) alters the catalytic activity for methanol synthesis. The calculated substitution energy shows that the indium atom tends to be doped at the step edge of Rh(211). Almost all species prefer to adsorb at the step-edge sites because the surface atoms at the step-edge possess the lowest coordination number. The electronic structure analysis demonstrates that the activation degree of CO2* chiefly relies on the charge transfer between CO2* and catalyst. Furthermore, the doped indium atoms make In/Rh(211) expose more H* adsorption sites and promote the relative stability of adsorbed species on In/Rh(211). Besides, the doping of indium significantly inhibits the generation of by-product CO*, and enables the activation barrier to be as low as 0.98 eV for the rate-determining step on In/Rh(211), which is much lower than that of some reported catalysts. The ultrahigh catalytic activity of In/Rh(211) might be attributed to the decrease of the work function induced by the doping of indium, enhancing the relative stability of reaction species and CO2* activation degree.

Direct synthesis of CuO–ZnO–CeO2 catalyst on Al2O3/cordierite monolith for methanol steam reforming

Methanol steam reforming (MSR) is a promising process for in-situ hydrogen production in vehicles. However, designing monolithic catalysts with high activity and selectivity as well as low pressure drop remains a challenge. In this work, CuO–ZnO–CeO2 catalysts were prepared directly on Al2O3/cordierite monolith through a sol-gel combustion method, and the effects of different combustion temperatures on the physicochemical properties and catalytic performance of the catalysts were investigated. It is demonstrated that the catalyst (CZC-400) prepared by combustion temperature at 400 °C is uniformly distributed on the Al2O3/cordierite monolith with smaller average catalyst particle size (4.2 nm) and higher specific surface area (23.7 m2 g−1). In the MSR, methanol conversion of CZC-400 reaches 100% at 260 °C without by-product CO. Furthermore, no significant change in the catalytic activity is observed during 32 h of the reaction. These results indicate that CZC-400 has the excellent catalytic activity and stability in the MSR.

Surface Structure Engineering of PdAg Alloys with Boosted CO2 Electrochemical Reduction Performance

Converting carbon dioxide into high-value-added formic acid as a basic raw material for the chemical industry via an electrochemical process under ambient conditions not only alleviates greenhouse gas effects but also contributes to effective carbon cycles. Unfortunately, the most commonly used Pd-based catalysts can be easily poisoned by the in situ formed minor byproduct CO during the carbon dioxide reduction reaction (CRR) process. Herein, we report a facile method to synthesize highly uniformed PdAg alloys with tunable morphologies and electrocatalytic performance via a simple liquid synthesis approach. By tuning the molar ratio of the Ag+ and Pd2+ precursors, the morphologies, composition, and electrocatalytic activities of the obtained materials were well-regulated, which was characterized by TEM, XPS, XRD, as well as electrocatalytic measurements. The CRR results showed that the as-obtained Pd3Ag exhibited the highest performance among the five samples, with a faradic efficient (FE) of 96% for formic acid at -0.2 V (vs. reference hydrogen electrode (RHE)) and superior stability without current density decrease. The enhanced ability to adsorb and activate CO2 molecules, higher resistance to CO, and a faster electronic transfer speed resulting from the alloyed PdAg nanostructure worked together to make great contributions to the improvement of the CRR performance. These findings may provide a new feasible route toward the rational design and synthesis of alloy catalysts with high stability and selectivity for clean energy storage and conversion in the future.

Exploring the potential for biomethane production by the hybrid anaerobic digestion and hydrothermal gasification process: A review

For a cleaner and healthier planet, industries must decarbonize and move away from ‘take-make-waste’ linear economies to circular economies , in ways that maximize value and minimize negative environmental impact. Anaerobic digestion (AD) is a well-known technology used to process domestic and industrial wastes to produce biogas (mainly CH 4 ) but with large volumes of high moisture content digestate as by-product The digestate is both difficult and expensive to manage, often requiring more than half the operating cost of treatment plants. Hydrothermal gasification (HTG) can convert the recalcitrant digestate into renewable gases including CH 4 . So, for high carbon conversion a hybrid AD and HTG technology is an attractive solution. In the hybrid process , AD can be used to treat the wet biomass (an existing practice), and the liquid AD digestate can then be processed by HTG to optimize CH 4 yield. This paper reviews the pros and cons of the AD and HTG processes, examines the valorization of co-products, and assesses the potential of the hybrid process with additional information from other AD-thermochemical process hybrids that have widely reported economic feasibilities . • AD-HTG is an efficient process for sustainable energy production. • Hybrid AD-HTG results in higher power and CH 4 generation. • Benefits of recycling HTG products to higher energy density gases were discussed. • Valorization of by-product CO 2 to chemicals were discussed. • Current challenges and future directions of AD-HTG process were presented.

New black indium oxide\u2014tandem photothermal CO2-H2 methanol selective catalyst

It has long been known that the thermal catalyst Cu/ZnO/Al2O3(CZA) can enable remarkable catalytic performance towards CO2 hydrogenation for the reverse water-gas shift (RWGS) and methanol synthesis reactions. However, owing to the direct competition between these reactions, high pressure and high hydrogen concentration (≥75%) are required to shift the thermodynamic equilibrium towards methanol synthesis. Herein, a new black indium oxide with photothermal catalytic activity is successfully prepared, and it facilitates a tandem synthesis of methanol at a low hydrogen concentration (50%) and ambient pressure by directly using by-product CO as feedstock. The methanol selectivities achieve 33.24% and 49.23% at low and high hydrogen concentrations, respectively.

Removal of NO by carbon-based catalytic reduction bed loaded with Mn induced by dielectric barrier discharge at low temperature

The current paper reports on a newly developed DBD-Mn/FCRB hybrid system to explore the removal of NOx by reduction without adding reducing gas at low temperature (below 80℃). This technology was established with a fixed carbon-based reduction catalytic reduction bed loaded with manganese (Mn/FCRB) induced by dielectric barrier discharge (DBD). The NO conversion and N2 selectivity in the new hybrid system reached 90.9 and 79.9%, respectively under 8% oxygen content, 1,200 J/L specific input energy (SIE), which were all higher than in the single DBD and DBD-FCRB systems, respectively. The Mn/FCRB was further characterized before and after activation by SEM, XRD and XPS. The possible reaction pathways of denitration were proposed through three processes based on the experimental results: direct denitration of active carbon atoms excited by plasma, reduction by adsorptive C(N) and C(O) complexes on the FCRB surface, and the reaction of nitrogen oxides with by-product CO. In addition, the results also showed that the new in-situ reduction denitration system had strong oxygen shock resistance and water resistance.

Insights into the crucial role of a Zn promoter for methanol dehydrogenation to methyl formate over Cu(111) catalysts.

Zn-doped Cu(111) alloy (Cu3Zn(111)) and Cu(111) surfaces were built using density functional theory (DFT) calculations to investigate the role of the Zn promoter in the methyl formate (MF) synthesis by the direct dehydrogenation of methanol. The rate determining step (RDS) of the MF synthesis is the dehydrogenation of CH3O to CH2O on both the Cu3Zn(111) alloy and the Cu(111) surfaces. Nevertheless, the energy barrier of the RDS is 119.4 kJ mol-1 on the Cu3Zn(111) alloy surface, lower than that on the Cu(111) surface. Compared with the favorable CH3O-CH2O coupling on the Cu(111) surface, the CH3O-CHO coupling is kinetically favorable on the Cu3Zn(111) alloy surface. Moreover, the formation of the by-product CO is effectively suppressed over the Cu3Zn(111) alloy surface. In addition, the results of the d-band center show that the addition of the Zn promoter increases the electron density of copper atoms, which accounts for the reduction in the energy barrier for the CH2O formation and inhibition of the CO formation.

Monolith, Goodyear collaborate on tires

Goodyear Tire & Rubber has signed an agreement to evaluate Monolith’s carbon black as a reinforcement for tires. Monolith uses pyrolysis at its plant in Hallam, Nebraska, to turn methane into carbon black and hydrogen without generating by-product CO 2 . Monolith will begin next year building a much larger facility in Hallam that will have 194,000 metric tons (t) per year of carbon black and 275,000 t of ammonia capacity when it opens in 2025. Monolith says it expects to provide Goodyear with one-third of the plant’s output.

Experimental study on the influence of H 2 O vapor and O 2 for desulfurization and denitrification of the diesel exhaust in marine application by non‐thermal plasma

To improve the pollutant removal efficiency by non-thermal plasma (NTP), the effect of H2O vapor and O2 on removal efficiency of NO and SO2 as well as the reduction of CO was investigated in H2O/O2/SO2/NO/C3H6/CO2/N2 system. To analyse the reaction mechanism, the effects of H2O vapor and O2 on the emission intensity of O ( 3 p 5 P → 3 s 5 S 2 0 ) and O H ( A 2 ∑ + → X 2 ∏ ) were investigated. The experimental results show that the increase of H2O vapour (0%–9.8%) promotes the generation of OH radicals, increases the removal efficiency of NO from 18.9% to 57.3%, decreases the energy per NO removed from 449.0 to 148.1 eV/NO, increases SO2 removal efficiency from 4.8% to 35.3%, decreases the energy per SO2 removed decreases from 2784.0 to 582.9 eV/SO2, and reduces the generation of CO from 460 to 229 ppm. In the range of 0%–15%, the increase of O2 content promotes the formation of O radicals, increases the removal efficiency of NO from 8.5% to 54.2%, and decreases the energy per NO removed from 994.3 to 156.4 eV/NO. In the range of 0%–5%, increasing O2 content promotes SO2 removal efficiency from 8.7% to 24.8%, and decreases the energy per SO2 removed from 2485.7 to 876.6 eV/SO2. However, CO generation increases from 200 to 350 ppm with the increase of O2 in 0%–5% due to the incomplete oxidation of C3H6. In the range of 5%–15%, the increase of O2 produces more O radicals, decreases the removal efficiency of SO2 from 24.8% to 23.5% and the generates of CO from 350 to 311 ppm. This study is helpful for improving the efficiency of NTP for desulfurization and denitrification, while reducing the by-product CO.

Pd atomic layer coating enhances CO2 hydrogenation to CH3OH fuel on Cu@Pd(111) core-shell structure catalyst

CO2 hydrogenation to methanol can convert greenhouse gases and hydrogen into high value-added liquid fuels, which can be used as a promising hydrogen storage technology, it is of great significance for mitigating the greenhouse effect and energy crisis. In this paper, density functional theory is used to study the effect of Pd atomic layer coating on the activation energy barrier and selectivity in CO2 hydrogenation to methanol. The Pd atomic layer coating can effectively increase the adsorption strength of the intermediate substance and the catalyst surface, the adsorption energy of H* is increased from − 3.50 to − 3.63 eV, and the adsorption energy of COOH* increases by 0.59 eV, properly increasing the adsorption energy is conducive to the progress of catalysis. The Pd atom coating is conducive to the activation and hydrogenation of CO2 and the dissociation of hydrogen, the activation energy barrier of the rate-limiting step is reduced from 1.71 to 1.00 eV, and the energy barrier of H2 dissociation is reduced by 0.27 eV. Cu@Pd(111) enhanced the electron delocalization and increased the catalytic activity. Besides, Pd atom coating suppresses the production of by-product CO, the adsorption energy of CO* increased from − 0.77 to − 1.76 eV, and the energy barrier for CO* production increased by 0.80 eV, inhibition of by-products is conducive to further improved methanol selectivity.

Technoeconomic and Life Cycle Analysis of Synthetic Methanol Production from Hydrogen and Industrial Byproduct CO2.

CO2 capture and utilization provides an alternative pathway for low-carbon hydrocarbon production. Given the ample supply of high-purity CO2 emitted from ethanol and ammonia plants, this study conducted technoeconomic analysis and environmental life cycle analysis of several systems: integrated methanol-ethanol coproduction, integrated methanol-ammonia coproduction, and stand-alone methanol production systems, using CO2 feedstock from ethanol plants, ammonia plants, and general market CO2 supply. The cradle-to-grave greenhouse gas emissions of methanol produced from the stand-alone methanol, integrated methanol-ethanol, and integrated methanol-ammonia systems are 13.6, 37.9, and 84.6 g CO2-equiv/MJ, respectively, compared to 91.5 g CO2-equiv/MJ of conventional methanol produced from natural gas. The minimum fuel selling price (MFSP) of methanol ($0.61-0.64/kg) is 61-68% higher than the average market methanol price of $0.38/kg, when using a Department of Energy target renewable hydrogen production price of $2.0/kg. The methanol price increases to $1.24-1.28/kg when the hydrogen price is $5.0/kg. Without CO2 abatement credits, the H2 price needs to be within $0.77-0.95/kg for the MFSP of methanol to equal the average methanol market price. With a CO2 credit of $35/MT according to tax credit per metric ton of CO2 captured and used, the methanol price is reduced to $0.56-0.59/kg.

Theoretical exploration of VOCs removal mechanism by carbon nanotubes through persulfate-based advanced oxidation processes: Adsorption and catalytic oxidation

Carbon-catalyzed persulfate activation for the removal of gaseous volatile organic compounds (VOCs) has not been reported yet, and the corresponding fundamental mechanisms of VOCs adsorption and the subsequent VOCs degradation remain controversial. In this work, theoretical chemistry calculations were carried out to explore the VOCs removal mechanism by the persulfate-based advanced oxidation processes (P-AOPs) for VOCs removal over single walled carbon nanotubes (SWCNT). This study provided detailed theoretical insights into the SWCNT/P-AOPs for VOCs treatment in terms of adsorption, activation, mineralization, and diffusion of VOCs or peroxymonosulfate (PMS). Various VOCs were found to be preferentially adsorbed onto SWCNT, and the adsorption strength of VOCs was found to be significantly dependent on their polarizability. On the other side, PMS adsorbed on SWCNT could be efficiently activated through accepting π electron in the sp2 carbon matrix of SWCNT rather than the electrons at dangling bonds to generate •OH radicals attributed to the strong interaction between PMS and SWCNT. Formaldehyde was then taken as an example to evaluate the catalytic degradation pathways via SWCNT/P-AOPs. Under the attack of •OH radicals, the ultrafast degradation pathway of formaldehyde with no byproduct CO was identified with ultralow reaction energy barrier and large energy release. In addition, factors affecting the adsorption of organic compounds were identified and the detailed PMS activation pathway was present directly in this work. Above all, this work extended the carbons/P-AOPs system to VOCs abatement and presented systematic evidences for the essential mechanisms associated with VOCs adsorption and PMS activation by SWCNT, and the corresponding removal pathway and mechanism were also understood.

Effect of EDTA-2Na modification on Fe-Co/Al2O3 for hydrogenation of carbon dioxide to lower olefins and gasoline

Capturing and utilization of carbon dioxide (CO2) not only leads to effective use of carbon resources, but also alleviates environmental pollution caused by increasing concentration of CO2, thus making it a hot research topic in recent years. In this study, a series of highly dispersed iron-cobalt (Fe-Co) catalysts was prepared by ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) modification, which could efficiently convert CO2 into high value-added chemicals (C2-C4= and C5-C11). X-ray diffraction (XRD) analysis showed that the addition of a small amount of Co and EDTA-2Na contributed to enhance the sintering resistance of Fe species. During the calcination process, EDTA4− can be decomposed into small organic molecules with reducibility, thus promoting the reduction of iron species. The CO temperature-programmed desorption (CO-TPD) results showed that cobalt enhanced the adsorption and activation of intermediate CO on NaxFe-Co catalyst, thereby promoting the catalytic conversion of CO2. The complexation of EDTA promotes the synergistic effect of Fe-Co bimetals, enhances the chemical adsorption of CO2. Sodium in EDTA-2Na promotes the surface basicity of the catalysts, which is favored for improving the product distribution of hydrocarbons. At lower H2/CO2 (1/1) ratio, the EDTA-2Na modified Fe-Co/Al2O3 catalyst exhibited high conversion of CO2 (32.8 %) and excellent selectivity toward high value-added chemicals. The selectivity of by-product CO was only 8.1 %; and C2-C4= (32.5 %) and C5-C11 (46.3 %) accounted for ∼79 % selectivity among the hydrocarbons generated.