CO2 Temperature-programmed Desorption Research Articles

Low temperature ethanol steam reforming: Selectivity control with lithium doping of Pt/m-ZrO2

Lithium promoted 2%Pt/m-ZrO2 catalysts previously observed to exhibit higher rates for the low temperature water-gas shift (LTS) were tested for the ethanol steam reforming with the aim of exploring the potential tuning of the selectivity. Characterization of catalysts having optimized Li content (0.5–0.75%Li) for LTS exhibited (a) weakened CH bonding of formate, a proposed intermediate in the LTS mechanism, as shown by a shift in the ν(CH) band to lower wavenumbers, (b) a relatively low extent of blocking of Pt, as measured by the ν(CO) band intensity of Pt-CO, (c) increased basicity as measured by CO2 temperature-programmed desorption with mass spectrometry, but not so high as to strongly inhibit CO2 product removal, and finally (d) no evidence of electron transfer from Li to Pt. Here, the same catalysts were tested for ethanol steam reforming (ESR). Results show that Li could likewise weaken the CC bond of the acetate intermediate, the analog of formate in LTS, and facilitate decarboxylation over decarbonylation altering the selectivity in favor of methanation. This trend was confirmed by fixed bed reaction testing, in-situ infrared spectroscopy experiments of transient ESR, and temperature-programmed ESR using MS. The Li-doped catalysts may be used to pre-reform ethanol prior to feeding to a methane steam reformer to increase the overall H2 selectivity of the process. DRIFTS of steady state ESR revealed that deactivation occurs through losses in the Pt-support interface, thereby hindering the turnover of the acetate intermediate.

Plasma-catalytic ammonia synthesis over BaTiO3 supported metal catalysts: Process optimization using response surface methodology

Non-thermal plasma (NTP) assisted ammonia (NH3) synthesis has been performed in a packed-bed dielectric barrier discharge (DBD) reactor. The presence of M/BaTiO3 (M = Fe, Co and Ni) catalysts in the DBD reactor significantly improved the NH3 concentration and energy efficiency with a sequence of Ni/BaTiO3 > Co/BaTiO3 > Fe/BaTiO3 > BaTiO3. Catalyst characterization, including N2 adsorption-desorption, X-ray diffraction analysis and temperature-programmed desorption of CO2, was performed to get insights into the relationships between the plasma-assisted NH3 synthesis process and M/BaTiO3 catalysts. The improved performance of plasma-assisted NH3 synthesis over Ni/BaTiO3 could be attributed to abundant basic sites and weaker metal-nitrogen (M-N) binding on its surfaces, which benefit the generation of NHx species and desorption of formed NH3. Response surface methodology (RSM) was used to assess the contribution of each independent process parameter and explore their mutual effects on the NH3 synthesis process systematically. The results of analysis of variance (AVONA) suggested that plasma discharge power and gas flow rate were the most significant factors in affecting the NH3 concentration and energy efficiency of the plasma-assisted NH3 synthesis process, respectively. Based on the proposed polynomial regression model, the maximum energy efficiency of 2.37 g kWh−1 was achieved at the predicted optimal operating conditions over Ni/BaTiO3.

One pot sol-gel synthesis of Pt−Ni/TiO2 with high CO2 methanation catalytic activity at low temperature

In this work, 2 wt%Pt/TiO2, 20 wt%Ni/TiO2 monometallic catalysts and xwt%Pt−20 wt%Ni/TiO2 (x = 1, 2 and 4 wt%) bimetallic catalysts were synthesized by one-pot sol-gel method for CO2 methanation reaction. All bimetallic catalysts revealed higher CO2 conversion than both monometallic catalysts. The 2 wt%Pt−20 wt%Ni/TiO2 catalyst exhibited the highest percentage of CO2 conversion at low reaction temperature, with almost 100% CH4 selectivity and high stability during 72 h time on stream. The effect of Pt co-doped with Ni to bimetallic formed on the catalyst properties was studied using several techniques, including X-ray diffraction, N2 adsorption-desorption, Raman spectroscopy, transmission electron microscopy, field emission scanning electron microscopy, H2 temperature-programmed desorption, H2 temperature-programmed reduction, CO2 temperature-programmed desorption and X-ray absorption spectroscopy (both ex-situ and in-situ experiments). The results showed that Pt was dispersed on the catalyst surface in the form of platinum oxide, while Ni was both incorporated into the TiO2 lattice with the excess amount from saturated level being dispersed on the catalyst surface. The results from XAS evidenced that some electrons movement from Ni to Pt occurred. This electronic property changing can tune the interaction between Ni and TiO2 support with appropriate strength and then resulting in higher reducibility of the catalyst and higher dispersion of Ni species. Furthermore, the electron-rich Pt site on the catalyst surface favored to adsorb CO from CO2 dissociation and further activated adsorbed CO to interact with nearby hydrogen atoms to form CH4 leading to high CO2 methanation activity at low temperature.

Contribution of Na/K Doping to the Activity and Mechanism of Low-Temperature COS Hydrolysis over TiO2-Al2O3 Based Catalyst in Blast Furnace Gas

As an organic sulfur pollutant generated in blast furnace gas, carbonyl sulfide (COS) has attracted more attention due to its negative effects on the environment and economy. The TiO2-Al2O3 composite metal oxide (Ti0.5Al) with uniformly dispersed particles was prepared by the co-precipitation method. And on this basis, a series of Na/K-doped catalysts were prepared separately. The activity evaluation results showed that the introduction of Na/K significantly improved the low-temperature COS hydrolysis activity, which exhibited a COS conversion of 98% and H2S yield of 95% at 75 °C with 24,000 h–1. And K showed a better promoting effect than Na. Brunauer–Emmett–Teller (BET) results revealed the increased mesopore proportion of Na/K-modified catalysts. X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that Na and K formed prismatic and nanorod-like structures, respectively. More weakly basic sites with enhanced intensity and decreased Oads/Olat content contributed to the excellent catalytic activity, as certified by the results of CO2 temperature-programmed desorption (CO2-TPD) and X-ray photoelectron spectroscopy (XPS). It was also proposed that the decrease of weakly basic sites ultimately deactivated catalyst activity. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that the introduction of Na/K enhanced the dissociation of H2O, and the generated abundant hydroxyl groups promoted the adsorption of COS and formed surface transition species, such as HSCO2– and HCO3–.

Strain-assisted in-situ formed oxygen defective WO3 film for photothermal-synergistic reverse water gas shift reaction and single-particle study

Among the reactions about CO2 conversion, the reverse water gas shift (RWGS) reaction is an efficient method to convert CO2 to CO. Herein, by the assistance of strain and introduction of light and reactant, in-situ formed oxygen defective WO3 film was synthesized, as an effective catalyst for reverse water gas shift reaction with an intense photothermal-synergistic effect. Furthermore, the in-situ single-particle Time-Resolved Photoluminescence (TRPL) and Photoluminescence (PL) spectrum were used to explore the details during the reaction, and prolonged charge carrier lifetime and significantly enhanced Photoluminescence intensities were observed in the in-situ single-particle study. Notably, the production rate of CO for WO3 film is almost 10 times that of powder, which means that WO3 film has an intense photothermal-synergistic effect. As proved by the results of CO2 temperature-programmed desorption (TPD) and CO2 adsorption, the oxygen vacancies are beneficial to the capture and activation of CO2, boosting the process of the reverse water gas shift. Meanwhile, lattice strain arising from the thermal expansion during the reaction could assist the in-situ formation of oxygen defects, enhance charge separation and regulate the electrical structure. All of this contribute to the synergy effect in photothermal reaction. Our work may provide a novel strategy for reasonable design of catalyst and illuminate the behavior of carriers in single-particle level.

Plasma-catalytic synthesis of ammonia over Ru-based catalysts: Insights into the support effect

In this work, we have investigated the effect of different supports (activated carbon (AC), α-Al2O3, ZSM-5 and SiO2) on the plasma-catalytic synthesis of ammonia (NH3) from N2 and H2 over Ru-based catalysts in a dielectric barrier discharge (DBD) plasma reactor. Compared with the NH3 synthesis using plasma alone, the presence of the Ru-based catalysts in the DBD reactor significantly enhanced the NH3 production and energy yield by 163%–387.6% with a sequence of Ru/AC > Ru/ZSM-5 > Ru/α-Al2O3 > Ru/SiO2. The effect of different operating parameters on the plasma-catalytic NH3 synthesis over Ru/AC was also examined. N2 adsorption-desorption experiment, X-ray diffraction analysis and temperature-programmed desorption of CO2 were performed to get insights into the structure-performance relationships between the plasma-catalytic NH3 synthesis and Ru-based catalysts with different supports. Both textural properties and the basicity of the Ru/AC catalyst contributed to the enhanced NH3 production in the hybrid plasma-catalytic system.

Oxidative coupling of methane on Li/CeO2 based catalysts: Investigation of the effect of Mg- and La-doping of the CeO2 support

The work presented herein reports on the oxidative coupling of methane (OCM) performance of a series of Li-free and Li-doped CeO2 and CeO2 modified with Mg2+ and La3+ catalysts. The supporting materials (Ce, Mg-Ce and La-Mg-Ce metal oxides) were synthesized using the microwave assisted sol-gel method, while lithium ions were added using the wet impregnation technique, to further affect the physicochemical properties, activity and selectivity of the materials, in terms of the desirable hydrocarbon products (C2H4 and C2H6). The materials were characterized towards their textural, structural and redox properties, surface basicity, and surface morphology using N2 adsorption/desorption, X-Ray Diffraction (XRD), Raman spectroscopy, CO2-Temperature Programmed Desorption (CO2-TPD), H2-Temperature Programmed Reduction (H2-TPR), Scanning Electron Microscopy (SEM), and X-ray Photoelectron Spectroscopy (XPS). Catalytic activity was assessed between 600 and 870 °C, at atmospheric pressure and different CH4:O2 molar ratios and Weigh-basis Gas Hourly Space Velocity (WGHSV). It is concluded that low specific surface area values, the existence of surface moderate basic sites, increased concentration of oxygen vacancies and the presence of electrophilic oxygen species (O2– and O22–) on the catalyst surface had a crucial role on the improvement of the catalytic performance in terms of the desirable products, mainly ethylene. It is noted that the addition of Li changed thoroughly the reaction pathway and the products’ distribution, with the C2 selectivity values exceeding 85%. The Li/Mg-Ce catalyst, presenting the higher population of intermediate basic sites and surface superoxide species, showed an improved catalytic activity in terms of XCH4 and production of ethylene, while the incorporation of La3+ into the crystal structure of CeO2 suppressed the production of ethylene. Finally, smaller CH4:O2 molar ratios suppressed the production of hydrocarbons, while enhanced residence times, favoured the dehydrogenation of C2H6 to C2H4.

Catalytic Performance of Li/Mg Composites for the Synthesis of Glycerol Carbonate from Glycerol and Dimethyl Carbonate.

A series of Li/Mg composites were synthesized by the coprecipitation method using magnesium and lithium nitrates, and then used for the synthesis of glycerol carbonate (GC) from glycerol and dimethyl carbonate (DMC). The experimental results indicated that Li/Mg composites were prospective catalysts for GC synthesis. 92.05% glycerol conversion and 90.61% GC yield were obtained after reacting at 80 °C for 2 h in the presence of Li/Mg composites. The structure and properties of Li/Mg composites were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Brunauer–Emmett–Teller (BET), and CO2–temperature-programmed desorption (TPD) techniques. It was inferred that the basic strength and basicity of Li/Mg composites were improved with increase in Li content. It was concluded that Li2CO3 was the main reactive species. A too-strong basic strength of Li/Mg composites could facilitate the glycerol conversion but impair GC selectivity.

Tuning the nitrogen contents in carbon matrix encapsulating Co nanoparticles for promoting formaldehyde removal through Mott-Schottky effect

The increment of N dopants in carbon matrix can effectively enrich the electron density of N-doped carbon encapsulating metal nanoparticles (NPs) via Mott-Schottky effect, thereby favoring the activation of molecular O2 with abundant free electrons on carbon surface. Herein, given the essential role of oxygen activation in formaldehyde (HCHO) oxidation, Co NPs-embedded nitrogen-doped carbon and carbon nanotubes (Co/NCNT) with controllable N contents (2.30 ~ 4.38 wt%) were prepared and utilized for catalytic oxidation of HCHO at room temperature. Electron transfer from the Co core to the N-doped carbon layer was modulated by the tailorable concentrations of N dopant through the Mott-Schottky effect at their interface, being validated by X-ray and ultraviolet photoelectron spectroscopy, as well as CO2 temperature-programmed desorption experiment. The catalytic activity increased gradually with the elevation of nitrogen content, achieving a HCHO removal efficiency of approximately 80% over Co/NCNT-5 with the maximum nitrogen content. Combined with the comprehensive characterizations, the mechanism underlying the catalytic activity improvement in HCHO oxidation induced by the Mott-Schottky effect was proposed. This work provides a new insight into optimizing the non-noble metal catalysts for HCHO oxidation at room temperature.

Reconstruction of the ZnAl Mixed Oxides Into the Layered Double Hydroxide Catalysts Active in the Aldol Condensation of Furfural: The Role of ZnO Particles.

A memory effect is the ability to restore the original, lamellar layered double hydroxide structure. Herein, we have described 1) the changes in the structural and basic properties of ZnAl mixed oxides during their transformation into ZnAl-reconstructed LDHs (RE-LDHs); 2) the extraordinary properties of ZnAl RE-LDHs compared to the original ZnAl LDHs; and 3) the changes of basic properties during the interaction of ZnAl RE-LDHs with atmospheric CO2. Aldol condensation was selected as probe reaction to prove the catalytic potential of ZnAl RE-LDHs. We have described a target method for preparing ZnAl RE-LDHs with a large number of basic sites. ZnAl RE-LDHs possess significantly higher furfural conversion in the aldol condensation of furfural than MOs. The structural, textural, and basic properties of the studied materials were described by temperature-programmed analysis, X-ray diffraction, N2 adsorption, temperature-programmed desorption of CO2, and in-situ diffuse reflectance spectroscopy.

Castor oil transesterification catalyzed by a new red mud based LiAlO2-LiFeO2 composite

In this study, a new low-cost LiAlO2-LiFeO2 composite (Li/RM) was prepared through a simple solid-state reaction using red mud (RM) as raw material, and the transesterification of castor oil with methanol for biodiesel production was carried out with the prepared Li/RM composite. The optimum preparation parameters of Li/RM composite were obtained, and the optimum preparation parameters were as follows: mass ratio of Li2CO3 to RM 2.5:1, calcination temperature 900 °C and calcination time 3 h. The synthetic catalysts were characterized by Thermogravimetric-Differential Thermogravimetric (TG-DTG), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Brunauer-Emmett-Teller method (BET) and CO2-Temperature programmed desorption (CO2-TPD). The biodiesel conversion of 96.32% was obtained under optimal parameters of reaction temperature of 65 °C, catalyst amount of 5 wt%, reaction time of 2.5 h and methanol/oil molar ratio of 15:1. Meanwhile, the kinetics and thermodynamics studies revealed that the transesterification reaction of castor oil obeyed the pseudo-first-order kinetics and was an endothermic, non-spontaneous reaction. The possible catalytic mechanism catalyzed by Li/RM catalyst was further investigated. Besides, the Li/RM composite had an excellent air tolerance and retained its good reusability after four cycles, indicating that Li/RM was an efficient and durable heterogeneous catalyst for biodiesel production.

Scalable combustion synthesis of copper-based perovskite catalysts for CO2 reduction to methanol: Reaction structure-activity relationships, kinetics, and stability

The selectivity of the CO2 hydrogenation can be tuned easily by altering the chemical Cu oxidation state, the correlated synergistic effect between copper, alkaline metal elements and support, and operation. In this mechanistic work, several perovskite-containing Cu/Sr/Ti materials were prepared, using one-step solution combustion method, by varying characteristic system parameters, including fuel selection relationship, maximal reference Cu loading, the type of deposition and the size of nanoparticles, Sr/Ti ratio, physical calcination temperature and the series of reactions. The activity under application was measured at relevant functional methanol synthesis conditions (200–280 °C, 20–50 bar and 8,000–24,000 h−1), validated to be stable, and connected with component physicochemical properties, identified applying X-ray powder diffraction (XRD), benchmarking and Rietveld refinement, N2 physisorption, the scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy- (EDS), the temperature-programmed reduction of H2 (H2 TPR), N2O pulsed surface oxidation (N2O PSO) and the temperature-programmed desorption of CO2 (CO2 TPD) interactions. Aqueous citric acid was assessed as the most suitable energy source; the optimal experimental heating was at 650 °C, balancing remaining nitrate ions, thermal sintering, and active Cu sites, while adsorption surface area was high. Additionally, a long-term stability determination test of the best-manufactured product (Cu5Sr3Ti2OX) was performed, deactivation was analysed, and derived kinetic model was constructed, which adequately described intrinsic catalytic behaviour over a broad operational range investigated. Graaf kinetics were assumed to be suitable for commercial Cu/ZnO/Al2O3, integrating the sorption, rates, and equilibrium into macro-kinetics, removing resistances of transport phenomena. Semiconductors as substrates facilitate the extrapolation of solar-driven photo-thermal catalysis.

Atomically dispersed Ru catalysts for polychlorinated aromatic hydrocarbon oxidation.

The development of cost-efficient catalysts with good catalytic activity is an urgent task for polychlorinated aromatic hydrocarbon (PCAH) oxidation. Herein, atomically dispersed Ru catalysts (denoted as Ru ADCs) proved by aberration corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption spectroscopy were synthesized for PCAH oxidation. The oxidation results showed that 0.2 Ru ADCs exhibited enhanced catalytic activity (T50% < 250 °C, T90% < 300 °C) compared with the T90% > 300 °C on 0.2 Ru nanoparticles (NPs). Besides, 0.2 Ru ADCs demonstrated high CO2 yield with >60% CO2ratio, along with good stability (>80% conversion for 800 mins). The better performance of 0.2 Ru ADCs was verified by kinetic experiments, in which, the apparent activation energy associated with 0.2 Ru ADCs (50.8 kJ mol-1) was significantly lower compared with that with 0.2 Ru NPs (80.0 kJ mol-1). The superior oxidation activity of 0.2 Ru ADCs was also applied to toluene oxidation. H2 temperature-programmed reduction ensured the stronger interaction of Ru species with the supports in Ru ADCs than that in Ru NPs, thus inhibiting Ru species aggregation and favoring their higher dispersion ensured by CO temperature-programmed desorption. The present work provides a potential strategy to maximize the usage of noble metal catalysts for PCAH oxidation.

SrCo0.4Fe0.4Zr0.1Y0.1O3-δ, A new CO2 tolerant cathode for proton-conducting solid oxide fuel cells

CO2 poisoning is not a negligible issue for SrCoO3-δ based materials, which limits their application as cathodes for solid oxide fuel cells (SOFCs). In this paper, iron, zirconium, and yttrium were co-doped into SrCoO3-δ to form a structurally stable cubic perovskite material, SrCo0.4Fe0.4Zr0.1Y0.1O3-δ (SCFZY). The CO2 adsorption-desorption on SCFZY was studied via X-ray diffraction and CO2 temperature-programmed desorption. The polarization resistance of the symmetric cell SCFZY|BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb)|SCFZY was tested in air containing 10 vol% CO2 to evaluate the SCFZY's CO2-tolerance as a SOFCs cathode. When applied as a SOFCs cathode in a cell with a proton-conducting electrolyte BZCYYb, SCFZY showed significant CO2-tolerance. The single-cell NiO-BZCYYb|BZCYYb|BZCYYb-SCFZY showed an output with a maximum power density of 679 mW cm−2 at 700 °C and good durability of 500 h. The SCFZY cathode also displayed better CO2-tolerance than the Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) cathode for IT- SOFCs.

Infrared reflection absorption spectroscopy and temperature-programmed desorption studies of CO adsorption on Ni/CeO2(111) thin films: The role of the ceria support

Ceria-supported Ni has shown unique catalytic activity due to unique properties of small Ni particles and strong metal-support interaction. Identification of adsorption sites and understanding the chemical interaction over Ni-ceria at the fundamental level provide crucial insights into the reaction pathways of complex catalytic processes. In this study, to probe the surface sites, the adsorption of CO was carried out with model Ni/ceria systems consisting of Ni nanoparticles vapor-deposited on well-ordered CeOx(111) (1.5 &amp;lt; x &amp;lt; 2) thin films using infrared reflection absorption spectroscopy (IRRAS) and temperature-programmed desorption (TPD) under ultrahigh vacuum (UHV) conditions. Fully oxidized CeO2(111) (Ce4+) and partially reduced CeO1.75(111) (Ce4+/Ce3+) thin films were grown on Ru(0001) to examine the role of the ceria support. Ni with low coverages (e.g., 0.2 ML) grows forming small two-dimensional particles on ceria at 300 K, which develop into three-dimensional clusters after heating to 700 K. In the absence of Ni, CO adsorption at 1 mTorr at 100 K shows distinct IR bands at 2158 cm−1 on CeO2 and 2165 cm−1 on CeO1.75. Bridging and atop IR bands associated with CO adsorption over metallic Ni were observed on the Ni-CeO1.75 surface at 300 K under UHV conditions. CO adsorption over Ni0 was also observed over as-deposited Ni on CeO2. However, a new IR band at 2146 cm−1 due to CO adsorption over Ni2+ species was detected at 100 K over the annealed Ni particles on CeO2. CO IRRAS data suggest the oxidation of Ni to Ni2+ on CeO2 and the formation of predominant Ni2+ species with heating, which is further confirmed with CO TPD data and previous x-ray photoelectron spectroscopy results.

Controlled Metal-Support Interactions in Au/CeO2-Mg(OH)2 Catalysts Activating the Direct Oxidative Esterification of Methacrolein with Methanol to Methyl Methacrylate.

The strong metal–support interaction (SMSI) between the three components in Au/CeO2–Mg(OH)2 can be controlled by the relative composition of CeO2 and Mg(OH)2 and by the calcination temperature for the direct oxidative esterification of methacrolein (MACR) with methanol to methyl methacrylate (MMA). The composition ratio of CeO2 and Mg(OH)2 in the catalyst affects the catalytic performance dramatically. An Au/CeO2 catalyst without Mg(OH)2 esterified MACR to a hemiacetal species without MMA production, which confirmed that Mg(OH)2 is a prerequisite for successful oxidative esterification. When Au/Mg(OH)2 was used without CeO2, the direct oxidative esterification of MACR was successful and produced MMA, the desired product. However, the MMA selectivity was much lower (72.5%) than that with Au/CeO2–Mg(OH)2 catalysts, which have an MMA selectivity of 93.9–99.8%, depending on the relative composition of CeO2 and Mg(OH)2. In addition, depending on the calcination temperature, the crystallinity of the CeO2–Mg(OH)2 and the surface acidity/basicity can be remarkably changed. Consequently, the Au-nanoparticle-supported catalysts exhibited different MACR conversions and MMA selectivities. The catalytic behavior can be explained by the different metal–support interactions between the three components depending on the composition ratio of CeO2 and Mg(OH)2 and the calcination temperature. These differences were evidenced by X-ray diffraction, X-ray photoelectron spectroscopy, and CO2 temperature-programmed desorption. The present study provides new insights into the design of SMSI-induced supported metal catalysts for the development of multifunctional heterogeneous catalysts.

Production of 5-Hydroxymethylfurfural from glucose using Al2O3-TiO2-ZrO2 ternary catalysts

In this work, mixed oxides Al2O3-TiO2-ZrO2 were evaluated varying their composition (% w/w) for the conversion of monosaccharides (fructose and glucose) to 5-hydroxymethylfural (HMF). Materials were characterized using Thermogravimetric Analysis and Differential Scanning Calorimetry (TGA-DSC), Nitrogen Physisorption (N2), X-ray Diffraction (XRD), RAMAN Spectroscopy, DRS UV-Vis Spectroscopy, Infrared Spectroscopy (FTIR), SEM, TEM, FTIR-Pyridine and Temperature Programmed Desorption of CO2 (TPD-CO2). The reactions were carried out at 175 °C and 30 bar of Ar pressure in a biphasic system (THF/H2O) for 3 h, obtaining a 78% maximum yield of HMF from the glucose and 63% yield from fructose. The materials studied carried out a direct dehydration of the monosaccharides to HMF in 30 min of reaction and were obtained as intermediates to dehydrate levulinic acid (LA) and formic acid (FA), these intermediates were analyzed and eluted using 1H NMR technique.

Mg2+ embedded MIL‐101(Cr)‐NH2 framework for improved CO2 adsorption and CO2/N2 selectivity

AbstractThe development of a CO2‐selective adsorbent with high CO2 uptake capacity and CO2/N2 selectivity is a challenge. In this work, Mg2+‐embedded MIL‐101(Cr)‐NH2 frameworks (Mg@MCrN) were simply prepared via a facile one‐step synthesis. The results indicated that the incorporation of a proper amount of Mg2+ into the host MIL‐101(Cr)‐NH2 increased the porosity of the resultant adsorbent. Noticeably, the temperature‐programmed desorption of CO2 (TPD‐CO2) analysis revealed that the prepared Mg@MCrN contained new metal active sites along with coordinately unsaturated Cr(III) sites and amine (NH2) sites of the framework. At 100 kPa and 25 oC, the prepared Mg@MCrN‐0.2 exhibited the highest CO2 uptake capacity and CO2/N2 selectivity of ca. ~3.04 mmol.g‐1 and ca. ~ 60, respectively, surpassing the parent MOF and many other CO2 benchmark adsorbents. Moreover, the CO2 adsorption capacity over the Mg2+‐incorporated MIL‐101(Cr)‐NH2 remained even after 5 cycles of adsorption‐desorption under pressure swing from 0 to 100 kPa. This work opens a new perspective for developing efficient CO2‐selective materials.

Facet-Dependent selectivity of CeO2 nanoparticles in 2-Propanol conversion

CeO2 nanoshapes, cubes with dominant (100) facets and octahedra with dominant (111) facets, were synthesized to investigate the influence of surface structure on acid-base properties. An optimization of calcination temperatures, coupled with Raman and TEM, was employed to minimize the intrinsic (Frenkel-type) defect sites and their potential complications on the facet studies involved in this work. The acid-base properties of these CeO2 nanoshapes were characterized with in situ pyridine and CO2 adsorption using infrared spectroscopy and quantified using pyridine, ammonia, and CO2 temperature-programmed desorption (TPD). The (100) facet displayed weaker acid sites with lower site density than the (111) facet which had a similar density of base sites but those on the (100) facet were stronger. A strong correlation was observed between 2-propanol conversion and each facet’s acid-base properties. CeO2 cubes exhibited greater base-site catalyzed dehydrogenation to acetone while the more acidic CeO2 octahedra were more active in dehydration to propene.

Bimetallic metal organic framework-templated synthesis of a Cu-ZnO/Al2O3 catalyst with superior methanol selectivity for CO2 hydrogenation

It is highly desirable to develop inexpensive and highly selective catalyst for CO2 hydrogenation to methanol and Cu/ZnO/Al2O3 is a promising formulation. Herein, we report the design and synthesis of a Cu-ZnO/Al2O3 catalyst via a bimetallic metal organic framework (MOF)-templated strategy (termed Cu-ZnOMOF⊂Al2O3) and shed light on the role of the Cu-Zn@MOF precursor in this system for methanol synthesis. The developed Cu-ZnOMOF⊂Al2O3 exhibited high methanol selectivity (86.9%) and methanol space-time yield (407.2 gMeOH•kgcat−1•h−1) at higher CO2 conversion (9.1%) in comparison with the conventional Cu-ZnONO3/Al2O3 catalyst (79.6% and 209.0 gMeOH•kgcat−1•h−1, and 5.1%, respectively) at 240 ºC under 3.0 MPa. Spectroscopic characterization (TEM, XPS, EDX, in-situ DRIFTS) coupled with N2O chemisorption and temperature-programmed desorption of CO2 and H2 revealed that the surface of the new Cu-ZnOMOF⊂Al2O3 catalyst possesses higher Cu dispersion, surface-enriched ZnO and more Cu-ZnO interfacial sites, which leads to higher capability for CO2 and H2 adsorption and activation. These are considered to be the origin of higher methanol selectivity and enhanced activity of the catalyst prepared by the MOF-templated strategy for CO2 hydrogenation. This work offers a novel approach to optimizing Cu-ZnO/Al2O3 catalyst for CO2 hydrogenation to methanol.