High Surface Area CeO2 Research Articles

Enhancing photocatalytic tetracycline degradation through the fabrication of high surface area CeO2 from a cerium-organic framework.

Water pollution is a global environmental issue, and the presence of pharmaceutical compounds, such as tetracyclines (TCs), in aquatic ecosystems has raised growing concerns due to the potential risks to both the environment and human health. A high surface area CeO2 was prepared via atmospheric thermal treatment of a metal-organic framework of cerium and benzene-1,3,5-tricarboxylate. The effects of calcination temperature on the morphology, structure, light absorption properties and tetracycline removal efficiency were studied. The best activity of the photocatalysts could be achieved when the heat treatment temperature is 300 °C, which enhances the photocatalytic degradation performance towards tetracycline under visible light. The resulting CeO2 particles have high capacity for adsorbing TCs from aqueous solution: 90 mg g-1 for 60 mg L-1 TCs. As a result, 98% of the initial TC can be removed under simulated sunlight irradiation. The cooperation of moderate defect concentration and disordered structure showed tetracycline removal activity about 10 times higher than the initial Ce-MOF. An embryotoxicity assessment on zebrafish revealed that treatment with CeO2 particles significantly decreased the toxicity of TC solutions.

Graphene oxide boosted high surface area CeO2 for humidity sensing

Precise measurement of humidity is of high significance in diverse fields like instrumentation, automated systems, agriculture and climatology. Herein as a first ever attempt, we report ceria-graphene oxide (CeO2-GO) composites as resistive type humidity sensor, that shows attractive response to moisture. High surface area ceria is synthesised via ammonia mediated precipitation from salt precursor, and CeO2-GO composites are achieved via hydrothermal route. The composites are well characterized using various analytical tools. Experiments using different mass ratios of GO in the composite show that there is an optimum amount of GO to realise maximum efficiency in the test parameters. It is further noted that the performance of the sensor is controlled by the active adsorption sites, which is proportional to surface area of the composite. An optimized CeO2-GO matrix yielded a response and recovery time of 19 s and 10 s respectively. The narrow hysteresis in moisture adsorption-desorption study and excellent stability for about 60 days are also observed for the system, warranting the successful utility of the system for practical applications.

Very high loading oxidized copper supported on ceria to catalyze the water-gas shift reaction

To prepare supported catalysts with high loading and high dispersion of active metals is a crucial challenge in heterogeneous catalysis. Here we report the fabrication of very reactive catalyst that contains finely dispersed copper with 20 wt% content supported on high-surface area CeO2 for the water–gas shift (WGS) reaction. This copper-ceria catalyst shows superb activity with a CO consumption rate of 116.7 μmolCO gcat-1 s−1 at 300 ℃, nearly one order of magnitude more active than other copper-based catalysts ever reported. Based on the precise and integratedcharacterizations, the oxidized not the metallic Cu are proved to be active centers where the adsorbed CO directly reacted with bridged —OH groups to finish the WGS reaction. The oxidized Cu sites are confirmed to be originated from the activation effect from Cu to CeO2, which promotes the oxygen of CeO2 diffuse from the bulk to surface, making Cu oxidized even under reductive atmosphere.

Visible light assisted production of methanol from CO2 using CdS@CeO2 heterojunction

The production of methanol from CO2 is highly desirable in present scenario due to the excessive CO2 emission. Several photocatalytic materials have been developed for reduction of CO2 into methanol under mild conditions, but things need to be developed soon. In the present work, the solvothermal process had synthesized high surface area CeO2 supported CdS nanocomposite. The catalytic amount of CdS@CeO2 heterojunction materials was highly active to produce methanol and CO from CO2. CdS@CeO2 heterojunction demonstrated a good formation of methanol (1534 μmol-g−1) and CO (213 μmol-g−1) under similar conditions. CdS@CeO2 heterojunction materials were studied using several characteristic techniques, such as XRD, XPS, HR-TEM, UV–vis, FTIR, PL, and Raman spectroscopy, physisorption and EIS analysis. CdS@CeO2 nanocomposite demonstrated excellent activity and stability with no leaching of metal content at the end of the sixth run.

Effect of Ni particle size on the production of renewable methane from CO2 over Ni/CeO2 catalyst

Production of ‘renewable Methane’ has attracted renewed research interest as a fundamental probe reaction and process for CO2 utilization through potential use in C1 fuel production and even for future space exploration technologies. CO2 methanation is a structure sensitive reaction on Ni/CeO2 catalysts. To precisely elucidate the size effect of the Ni metal center on the CO2 methanation performance, we prepared 2%Ni/CeO2 catalysts with pre-synthesized uniform Ni particles (2, 4 and 8 nm) on a high surface area CeO2 support. Transmission electron microscopy (TEM) and ambient pressure X-ray photo spectroscopy (AP-XPS) characterization have confirmed that the catalyst structure and chemical state was uniform and stable under reaction conditions. The 8 nm sized catalyst showed superior methanation selectivity over the 4 and 2 nm counterparts, and the methanation activity in term of TOF is 10 times and 70 times higher than for the 4 and 2 nm counterparts, respectively. The DRIFTS studies revealed that the larger Ni (8 nm particles) over CeO2 efficiently facilitated the hydrogenation of the surface formate intermediates, which is proposed as the rate determining step accounting for the excellent CO2 methanation performance.

FTIR investigation under reaction conditions during CO oxidation over Ru(x)-CeO2 catalysts

New insight on the understanding of the reaction mechanisms during the CO oxidation over Ru-containing CeO2 catalysts was reported. A set of ruthenium high surface area CeO2 oxides, with two different Ru loadings, was prepared for studying the evolution of Ru and Ce species during CO oxidation reaction, using a reaction mixture of 1 % CO, 0.5 % O2, N2 balance and a contact time W/FCO = 7.4 gcat h molCO−1. The samples were characterized by SBET, XRD, DRS UV–vis, TPR, Raman spectroscopy, and XPS. Furthermore, the samples were investigated by FTIR measurements during CO oxidation under reaction conditions. The catalysts with low Ru loading (1.5 wt.%) presented higher catalytic activity than those containing a higher Ru loading (3 % wt.). The catalytic activity test results strongly depend on electronic changes observed at the interface/surface of ceria support. The characterization results and FTIR investigation during CO oxidation show that the presence of ruthenium species modifies the electronic properties of the ceria surface promoting a change at their surface where a redox-mechanism was detected. This causes the formation of surface oxygen vacancies which promotes oxygen mobility from the ceria lattice contributing to the CO oxidation. The ruthenium incorporation drastically favors the CO adsorption (carbonyl and dicarbonyl species). However, our FTIR data not shown a direct correlation between the ruthenium-carbonyl species (linear and bridged form) on the CO transformation. Further, the presence of ruthenium enhances the formation of surface oxygen vacancies, which favor the oxygen mobility from the ceria lattice toward the CO oxidation. It was found that at low temperatures (close down to the maximum conversion), the CO oxidation preferably happened on oxygen vacancy sites.

Efficient and ecofriendly route for the solvent-free synthesis of piperonal and aromatic aldehydes using Au/CeO2 catalyst

In this work, an eco-friendly process for piperonal synthesis from piperonyl alcohol oxidation was developed. Piperonal was obtained with 100% selectivity under solvent free conditions, using air as oxidant at atmospheric pressure. The preparation of high surface area CeO2 using a surfactant-template method allowed the preparation of a catalyst with highly dispersed Au nanoparticles having an average diameter of about 1nm. The obtained results, using Au/CeO2 catalysts, suggested that the reaction network consists in the rapid oxidation of piperonyl alcohol to piperonal. Increasing reaction time to promote alcohol conversion a very small amount of formed aldehyde undergoes to further oxidation to the acid. Subsequently, piperonylic acid can easily react with the alcohol, leading to the formation of the ester that can be adsorbed on the catalyst surface, deactivating the materials. Nevertheless, the fine-tuning of the process, using solvent free conditions, air and low reaction time, demonstrated the possibility to control catalyst deactivation. Indeed, gold supported on nano-CeO2 were able to catalyse the production of piperonal without by-product formation, with 35% of piperonyl alcohol conversion after 45min of reaction and the catalyst can be recycled without any activity loss, demonstrating the possibility of scaling up a low conversion continuous process or low reaction time batch process.No toxic reagents were used neither for catalysts preparation nor for catalytic tests and the use of air as oxidant improved the safety of the process. The latter, together with the absence of a solvent, can led to important advancements in the industrial applications reducing the costs of the purification section. This versatile approach, interesting from both the economic and the environmental point of view, was also applied in the synthesis of other aromatic aldehydes, such as benzaldehyde, vanillin and anysil aldehyde, highlighting the importance of this process.

Hydrothermally Synthesized Ceria with a High Specific Surface Area for Catalytic Conversion of Ethanol to Ethylene

Morphological control can be used to improve the catalytic activity of cerium oxide (ceria, CeO2). In this study, ceria with a high specific surface area was synthesized via the hydrothermal reaction of ceric nitrate and was tested for the catalytic conversion of ethanol to ethylene. As a reference, ceria was also synthesized via a precipitation reaction of cerous nitrate using aqueous ammonia. The Japan reference catalyst JRC-CEO-1 also served as a reference. The specific surface area of the hydrothermally synthesized ceria was as high as that of JRC-CEO-1, but was much higher than that of either reference after calcination at 873 K. Thermogravimetric analysis and IR spectroscopy revealed that the cerias made by hydrothermal and precipitation reactions consisted of high-purity CeO2, whereas JRC-CEO-1 contained 1.5% decomposable functional groups (OH-, CO3 2-). For both ethanol conversion and ethylene selectivity in a catalytic dehydration reaction of ethanol, the activity of the hydrothermally developed ceria was higher than that for either reference. The reaction pathway for the dehydration reaction of ethanol over ceria showed that the specific surface area and the basicity of the Lewis basic sites of the ceria were influential properties. The high catalytic activity of the hydrothermally synthesized ceria was derived from its high specific surface area and high-purity CeO2.

Sm doped mesoporous CeO2 nanocrystals: aqueous solution-based surfactant assisted low temperature synthesis, characterization and their improved autocatalytic activity

Mesoporous Sm(3+) doped CeO2 (Ce-Sm) with a nanocrystalline framework, a high content of Ce(3+) and surface area (184 m(2) g(-1)), have been synthesized through a facile aqueous solution-based surfactant assisted route by using inorganic precursors and sodium dodecyl sulphate as a template. The XRD results indicate that the calcined Ce-Sm and even the as-prepared material have a cubic fluorite structure of CeO2 with no crystalline impurity phase. XRD studies along with HRTEM results confirmed the formation of mesoporous nanocrystalline CeO2 at a lower temperature as low as 100 °C. A detailed analysis revealed that Sm(3+) doping in CeO2 has increased the lattice volume, surface area, mesopore volume and engineered the surface defects. Higher concentrations of Ce(3+) and oxygen vacancies of Ce-Sm resulted in lowering of the band gap. It is evident from the H2-TPR results that Sm(3+) doping in CeO2 strongly modified the reduction behavior of CeO2 by shifting the bulk reduction at a much lower temperature, indicating increased oxygen mobility in the sample which enables enhanced oxygen diffusion at lower temperatures, thus promoting reducibility, i.e., the process of Ce(4+)→ Ce(3+). UV-visible transmission studies revealed improved autocatalytic performance due to easier Ce(4+)/Ce(3+) recycling in the Sm(3+) doped CeO2 nanoparticles. From the in vitro cytotoxicity of both pure CeO2 and Sm(3+) doped CeO2 calcined at 500 °C in a concentration as high as 100 μg mL(-1) (even after 120 h) on MG-63 cells, no obvious decrease in cell viability is observed, confirming their excellent biocompatibility. The presence of an increased amount of surface hydroxyl groups, mesoporosity, and surface defects have contributed towards an improved autocatalytic activity of mesoporous Ce-Sm, which appear to be a potential candidate for biomedical (antioxidant) applications.

Low‐Lanthanide‐Content CeO2/MgO Catalysts with Outstandingly Stable Oxygen Storage Capacities: An In‐Depth Structural Characterization by Advanced STEM Techniques

AbstractA novel CeO2/MgO catalyst with low ceria loading has been synthesized. This catalyst showed unique redox properties compared with conventional high and low surface area CeO2. Advanced (scanning) transmission electron microscopy techniques revealed the presence of a variety of highly dispersed ceria nanostructures: isolated CeOx entities, CeO2 clusters, as well as fairly small (<5 nm) CeO2 nanoparticles. More interestingly, this CeO2/MgO catalyst showed outstanding stability in its redox response against high temperature aging treatments. Thus, after reduction in hydrogen at 950 °C and further oxidation at 500 °C, CeO2 reduction effects took still place at low temperatures, and no significant loss of oxygen storage capacity (OSC) was detected. Unique ceria‐bilayer nanostructures were found and characterized in the aged catalyst. Their peculiar structural and chemical properties seem to be responsible for the large improvement observed in the stability of the redox response.

Evaluation of Co, La, and Mn promoted Rh catalysts for autothermal reforming of commercial diesel: Aging and characterization

In this study, three bimetallic catalysts are evaluated for autothermal reforming (ATR) of fuels (1wt.% Rh and 6wt.% X (X=Co, La or Mn) supported on high-surface area CeO2–ZrO2). The catalysts are aged for approximately 35h and carefully characterized both as fresh and aged materials. The objective is to illuminate the changes in material properties after time on stream as well as the differences among the materials. The changes in material properties are evaluated by H2-TPR, BET surface area analysis, TEM, SEM, and STEM. The material’s tendency to coke is investigated by TPO analysis.The three materials exhibit promising initial activity. However, the Co-promoted sample decreases sharply in activity after 25h of operation. Meanwhile, the other two materials display a more stable activity throughout the evaluated time. The deactivation of the Co-promoted material could be linked to the high amount of coke deposited during operation. Based on the results from the activity evaluation and characterization, the material promoted with lanthanum displays the most promising results. The addition of lanthanum resulted in a catalyst that was both stable and had high activity, even though a low rhodium loading is used. The material also shows superior thermal resistance compared to the other two materials. In addition, the tendency to coke is significantly lower compered to the other materials, which is especially beneficial when dealing with ATR of complex fuels.

Continuous catalytic upgrading of ethanol to n-butanol and >C4 products over Cu/CeO2 catalysts in supercritical CO2

Direct production of BuOH from EtOH is compared over four Cu catalysts, supported on different solid acids. The activity of these catalysts to perform the Guerbet reaction was assessed using a continuous flow reactor and the effect of using scCO2 was also monitored. Cu on high surface area CeO2 showed the best activity for BuOH formation, with yields above 30%.

Small CuO clusters on CeO2 nanospheres as active species for catalytic N2O decomposition

High surface area CeO2 nanospheres as an active catalyst support were synthesized using glycothermal approach. Different loadings of copper (4, 6, 10 and 15wt.%) were supported by wet impregnation method. Prepared materials were characterized by means of TEM, SEM-EDX, XRD, UV-Vis diffuse reflectance, N2 adsorption/desorption, DRIFT and H2-TPR techniques, and tested for the catalytic reaction of nitrous oxide decomposition. The best activity in the N2O degradation was found for the sample containing 10wt.% of Cu that can be attributed to the highest number of small CuO clusters on the catalyst surface. Further increase of copper content strongly affects the dispersion and leads to the formation of less active segregated CuO phase, which was confirmed by XRD, UV-Vis and H2-TPR results. Accordingly to UV–Vis examination and DRIFT analysis using CO as a probe molecule, all solids contain Cu+1 ions which play a crucial role in the N2O decomposition mechanism. The synthesized catalysts were also tested in wet or NO containing atmospheres, where an inhibiting effect takes place and leads to shifting of conversion profiles to higher temperature by 65 and 10°C, correspondingly. It was found out that the formation of a new, crystalline CuO·3H2O phase occurs in water vapour containing atmosphere, which can result in catalyst deactivation. However, this effect is fully reversible and the catalyst is able to replenish initial activity in dry atmosphere. Potentiality of CuO/CeO2 materials in catalytic N2O decomposition in industrial processes was confirmed by long-term stability tests performed in the period of 50h in the presence of inhibiting gas components.

Highly selective copper nanoparticles for the hydrogenation of α,β-unsaturated aldehydes in liquid phase

Unsupported copper nanoparticles (CuNPs), 3–4nm in size, are obtained from the reduction of the corresponding metal chloride through an electron transfer from a lithium arenide. CuNPs are tested for the liquid phase hydrogenation of cinnamaldehyde in batch conditions by using H2. High activity and selectivity to cinnamyl alcohol (87%, at high conversion) are reached. When CuNPs are supported on MCM-41 and on high surface area CeO2, TEM and XRD characterization shows that the nanometric size of copper is retained. For the hydrogenation of crotonaldehyde or of cinnamaldehyde, CuNPs/MCM-41 and CuNPs/CeO2 are less active and less selective than unsupported nanoparticles. However the selectivity levels reached by these catalysts are higher than those obtained over noble metal (Au and Pt) based catalysts, tested under the same reaction conditions. The catalytic properties of supported and unsupported CuNPs would be related to the nanometric size of copper.

High Surface Area CeO2 Promoted Suzuki-Miyaura Cross-Coupling of Arylboronic Acids and Aryl Iodides

High surface area cerium oxide (240 m2/g) efficiently promoted the Suzuki–Miyaura cross-coupling of aryl iodides with arylboronic acids, in the absence of palladium or any other ­transition-metal catalyst. Excellent selectivity towards the cross-coupling product was observed. Cerium oxide could be recovered and reused at least three times without any loss of activity.

Facile Fabrication of Single Crystalline Ceria Nanoparticles for Photo-Responsive Applications

The present investigation is about fabrication of single-crystalline ceria (CeO2) nanoparticle by a hydrothermal route. High surface area CeO2 was synthesized with transformation of morphology from nanofibers to nanocubes in response to processing conditions. A steady variation of average nanocrystallite size ca. in the range 3.0-16.9 nm and a range of band gap energy from 2.6 to 2.9 eV were measured. The surface area of the nanoparticles varied in the range 16.0136.1 m2/g and the variation in surface area is attributed to the nature of packing of particles. The ceria nanofibers could generate 870.5 µmol of H2 in 3 h of irradiation.

Effect of synthesis parameters on morphology and activity of bimetallic catalysts in CO2–CH4 reforming

High surface area CeO2–ZrO2 (80/20wt.%) mixed oxide supports with superior reducibility were synthesized by two solvothermal approaches, hydrothermal aging in NH4OH aqueous solution and glycothermal aging in ethylene glycol. The materials aged in alkaline water at elevated temperature and pressure exhibit large crystallite sizes (roughly 30–40nm), and structural segregation of the CeO2 and ZrO2 crystal phases. The materials synthesized by reduction in ethylene glycol show properties of homogeneous solid solutions with highly developed nanocrystalline structure (an average crystallite size was estimated at about 6nm). Bare CeO2–ZrO2 supports were selected mostly on grounds of their reducibility for the subsequent homogeneous deposition coprecipitation with nickel and cobalt (3, 6, 12, 18wt.%) loadings. The bimetallic catalysts were thoroughly characterized and then examined in the catalytic CO2–CH4 reforming reaction. The materials which exhibited both small crystallite sizes of the employed support and small active bimetallic particles, demonstrated high catalytic activity and good resistance to carbon accumulation on the catalyst surface. Dry reforming process over catalysts bearing glycothermally aged supports revealed the simultaneous occurrence of reverse water gas shift reaction, whereas the hydrothermally prepared supports stimulate methane dehydrogenation reaction at higher temperatures; the occurrence of both reactions is influenced by the dispersion of active metal species.

Ni supported high surface area CeO2–ZrO2 catalysts for hydrogen production from ethanol steam reforming

The catalytic activity of nano-sized x%Ni/Ce0.74Zr0.26O2 (x = 0, 2, 10 and 20wt%) catalysts have been investigated to develop highly active catalysts for ethanol steam reforming (ESR) into hydrogen. The structure and surface properties of the catalysts were tested by XRD, TPR, HRTEM and BET surface areas. The effect of reaction temperature from 200 °C to 600 °C was studied in a flow system at atmospheric pressure with an ethanol/water molar ratio of 1 : 8. Selectivity was calculated for the catalytic products H2, CO, CO2 and CH4, as well as the intermediates C2H6, C2H4, C3H8, CH3CHO and CH3COCH3, at different reaction temperatures. It was found that complete conversion of ethanol with considerable amounts of H2 was obtained at 400 °C over all catalysts. H2 was produced at a very low temperature (200 °C) over 10% and 20% Ni loadings, while a maximum H2 selectivity (75%) is reached at 600 °C over the 2%Ni/Ce0.74Zr0.26O2 catalyst; this is most likely due to the small nickel particle size (2–4 nm) in 2%Ni, which results in enhancement of the metal–support interactions. Thermal decomposition of ethanol in an ethanol/water mixture under the same reaction conditions, but in the absence of catalyst, was also studied. HRTEM of the spent catalyst (8 h ESR) shows the deposition of carbon in the form of carbon nanotubes (CNTs).

Excellent sulfur resistance of Pt/BaO/CeO2 lean NOx trap catalysts

In this work, we investigated the NOx storage behavior of Pt/BaO/CeO2 catalysts, especially in the presence of SO2. High surface area CeO2 (∼110m2/g) with a rod like morphology was synthesized and used as a support. The Pt/BaO/CeO2 sample demonstrated slightly higher NOx uptake in the entire temperature range studied compared with Pt/BaO/γ-Al2O3. More importantly, this ceria-based catalyst showed higher sulfur tolerance than the alumina-based one. The time of complete NOx uptake was maintained even after exposing the sample to ∼3g/L of SO2. The same sulfur exposure, on the other hand, eliminated the complete NOx uptake time on the alumina-based NOx storage catalysts. TEM images show no evidence of either Pt sintering or BaS phase formation during reductive de-sulfation up to 600°C on the ceria-based catalyst, while the same process over the alumina-based catalyst resulted in both a significant increase in the average Pt cluster size and the agglomeration of a newly formed BaS phase into large crystallites. XPS results revealed the presence of about five times more residual sulfur after reductive de-sulfation at 600°C on the alumina-based catalysts in comparison with the ceria-based ones. All of these results strongly support that, besides their superior intrinsic NOx uptake properties, ceria-based catalysts have (a) much higher sulfur tolerance and (b) excellent resistance against Pt sintering when they are compared to the widely used alumina-based catalysts.

High temperature desulfurization over nano-scale high surface area ceria for application in SOFC

In the present work, suitable absorbent material for high temperature desulfurization was investigated in order to apply internally in solid oxide fuel cells (SOFC). It was found that nano-scale high surface area CeO2 has useful desulfurization activity and enables efficient removal of H2S from feed gas between 500 to 850°C. In this range of temperature, compared to the conventional low surface area CeO2, 80–85% of H2S was removed by nano-scale high surface area CeO2, whereas only 30–32% of H2S was removed by conventional low surface area CeO2. According to the XRD studies, the product formed after desulfurization over nano-scale high surface area CeO2 was Ce2O2S. EDS mapping also suggested the uniform distribution of sulfur on the surface of CeO2. Regeneration experiments were then conducted by temperature programmed oxidation (TPO) experiment. Ce2O2S can be recovered to CeO2 after exposure in the oxidation condition at temperature above 600°C. It should be noted that SO2 is the product from this regeneration process. According to the SEM/EDS and XRD measurements, all Ce2O2S forming is converted to CeO2 after oxidative regeneration. As the final step, a deactivation model considering the concentration and temperature dependencies on the desulfurization activity of CeO2 was applied and the experimental results were fitted in this model for later application in the SOFC model.