CO2 Temperature-programmed Desorption Research Articles

Biogas dry reforming over Li–Ni–Al LDH-derived catalysts

Biogas dry reforming or dry reforming of methane (DRM) is an alternative to produce hydrogen, in the context of development of sustainable routes for energy production, since this route uses CH4 and CO2, two greenhouse gases as reactants. However, the deactivation of catalysts due to carbon deposition and sintering is the main drawback of this reaction. In this work, with the aim of minimizing carbon formation and sintering during DRM, the effect of lithium as a promoter in catalysts Ni–Al derived from layered double hydroxides was investigated. The catalysts were prepared by co-precipitation and characterized by different techniques: BET surface area (SBET), X-ray diffraction (XRD), temperature-programmed reduction (TPR), CO2 and H2 temperature-programmed desorption (CO2-TPD and H2-TPD), Scanning Electron Microscopy (SEM-EDS), temperature-programmed oxidation (TPO). The catalytic tests were carried out in a fixed bed reactor using a synthetic biogas (60% CH4 and 40% CO2) in the temperature range of 500–750 °C. The incorporation of Li into the Ni–Al-LDH changed the reducibility and basicity of the catalysts. The Li2 sample containing an intermediary amount of Li (5 wt%) showed the highest reduction temperature and highest density of basic sites, which resulted in the smallest Ni crystallite size before and after the reactions. As a result, this catalyst presented the greater resistance to sintering and a lower rate of carbon produced. For the reaction carried out at 700 °C, only the Li2 catalyst remaining active during the test and reaching a maximum of 80% and a final CH4 conversion of 54% after 480 min of reaction, whereas CO2 conversion was higher than 90%. All other samples deactivated at different rates due to carbon deposition and sintering.

Multi-promoters modified CaO-based sorbent derived from mixed waste slag for long-term CO2 cyclic capture

Calcium looping, a carbon dioxide (CO2) capture technique, may provide an effective route to eliminate climate change brought by the steadily rising anthropogenic CO2 emissions. However, the key challenge for calcium looping is the sintering-induced decay over the numerous cycles for CaO-based sorbents. Herein, multi-promoters modified CaO-based sorbents, derived from the mixed waste slag of marble waste powder (MWP) and rare earth polishing powder wet slag (REPP), are prepared by a simultaneous hydrating and calcining process. The cyclic CO2 capture is explored by a thermogravimetric analyzer, and the promotion mechanism is investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, CO2 temperature-programmed desorption, and reaction kinetics fitting. Results indicate that the multicomponent promoters from the REPP, including CeO2, Ca12Al14O33, and LaPO4, enhance the carbonation cyclic activity of CaO from MWP. The best-performing MWP-REPP sorbent with 15 wt% REPP shows less than a 10 % drop decay and the CO2 carbonation conversion remains at 75 % (0.46 g CO2/g sorbent) after 50 repeated cycles. The excellent cyclic capture performance is attributed to the synergistic interaction between the promoters and CaO, where the CeO2 promoter owns abundant oxygen vacancies, and the Ca12Al14O33 and LaPO4 promoters provide the blocked effect, thus facilitating the CO2 sorption and inhibiting the CaO from sintering. This work presents useful guidance for improving the cyclic sorption stability of CO2 from waste slags.

Tri-reforming of methane over Ni/ZrO2 catalyst derived from Zr-MOF for the production of synthesis gas.

The increasing concentration of CO2 and CH4 in the environment is a global concern. Tri-reforming of methane (TRM) is a promising route for the conversion of these two greenhouse gases to more valuable synthesis gas with an H2/CO ratio of 1.5-2. In this study, a series of Zr-MOF synthesized via the solvothermal method and impregnation technique was used to synthesize the nickel impregnated on MOF-derived ZrO2 catalyst. The catalyst was characterized by various methods, including N2-porosimetry, X-ray diffraction (XRD), temperature programmed reduction (TPR), CO2-temperature programmed desorption (CO2-TPD), thermo-gravimetric analysis (TGA), chemisorption, field-emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM). Characterization results confirmed the formation of the Zr-MOF and nickel metal dispersed on MOF-derived ZrO2. Further, the tri-reforming activity of the catalyst developed was evaluated in a downflow-packed bed reactor. The various catalysts were screened for TRM activity at different temperatures (600-850°C). Results demonstrated that TRM was highly favorable over the NZ-1000 catalyst due to its desirable physicochemical properties, including nickel metal surface area (2.3 m2/gcat-1), metal dispersion (7.1%), and nickel metal reducibility (45%), respectively. Over the NZ-1000 catalyst, an optimum H2/CO ratio of ~ 1.6-2 was achieved at 750°C, and it was stable for a longer period of time.

Catalytic upgrading of Naomaohu coal pyrolysis volatiles over NiAl and NiLiAl oxides

Catalytic upgrading of volatiles is an essential technology to improve the product distribution of pyrolysis for the clean and efficient utilization of low-rank coals. In this work, novel acid-base bifunctional catalysts composed of Ni/Li/Al oxides were designed and prepared using LDH precursors with tunable chemical composition and structural properties. The catalysts were systematically characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), physisorption, NH3-temperature programmed desorption (NH3-TPD), CO2-temperature programmed desorption (CO2-TPD), H2-temperature programmed reduction (H2-TPR), and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). A two-stage fixed bed reactor was employed to evaluate the performance of the catalysts. Characterization results suggest that the crystal size of NiO and the surface area of the catalyst decreased with increasing Li content and decreasing Ni content in the catalyst, while the pore volume and pore diameter were positively correlated with Li content. Moreover, the addition of Li reduced the amount of weak acid sites and raised the amount of total basic sites. Consequently, the bifunctional catalysts boosted the yield of light tar and the contents of aromatics and phenols in tar. Specifically, with the highest total acid sites (569 μmol/g) promoting the cracking of heavy pitch components, Ni2.5Li0.5Al1 decreased the content of pitch in tar to 23.8 wt%, representing a 42.7 % drop from the corresponding non-catalytic pyrolysis. Accordingly, it improved the light tar yield to 7.2 wt%, which was 18 % higher than non-catalytic pyrolysis. 450 °C is identified as a suitable temperature for the catalytic upgrading of volatiles from Naomaohu coal; higher catalysis temperatures at 500 °C and 550 °C led to lower tar yield and lower phenols content, along with higher gas yield and more carbon deposition.

Revealing the effect of synthetic method on integrated CO2 capture and conversion performance of Ni-Na2ZrO3 bifunctional materials

Integrated CO2 capture and utilization by reverse water gas shift (ICCU-RWGS) reaction for syngas production for C1 chemical industry has gained increasing attention. Designing highly active bifunctional materials that enables CO2 adsorption and in-situ conversion is essential. In this work, Ni-Na2ZrO3 bifunctional materials are prepared by different synthetic methods for ICCU-RWGS. N2 physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), CO2 temperature-programmed desorption (CO2-TPD) and H2 temperature-programmed reduction (H2-TPR) analysis reveals that Ni-Na2ZrO3-CP prepared by the co-precipitation (CP) method shows small Ni crystalline size, moderate surface basicity, and excellent reducibility. ICCU-RWGS performance is investigated under isothermal conditions of 650 °C, 10 %CO2 and 35 %H2. The results indicate that Ni-Na2ZrO3-CP demonstrates excellent performance in ICCU-RWGS, with a notable CO2 capture capacity of 3.76 mmol CO2/g and a CO production rate of 3.10 mmol CO/g. Additionally, it exhibits relatively good operational stability. Detailed reaction paths of the ICCU-RWGS procedure for the Ni-Na2ZrO3 bifunctional materials are proposed. The findings will shed new perspectives on the design of synthetic bifunctional catalysts for ICCU-RWGS.

Facet and dual vacancy engineering-boosting BiOBr for enhanced CO2 and epoxide cycloaddition reaction under mild and cocatalyst-free conditions: Double substrate active sites and activated surface bromine ions synergy

Among the many strategies for CO2 resource utilization, the synthetic technology of cyclic carbonates with 100 % atom economy through CO2and epoxide is one of the most industrially viable routes, but its efficiency has been severely hampered by the lack of highly active catalytic sites. Moreover, due to the intrinsic thermodynamic stability and kinetic inertia of CO2 and the higher energy barrier of the ring-opening reaction of epoxides, the heterogeneous catalytic conversion of CO2 highly depends on harsh operating conditions, high temperatures and pressures, and the incorporation of cocatalysts. The development of efficient heterogeneous catalysts for CO2 conversion under cocatalyst-free and mild conditions has always been a challenge. Herein, we have proposed a synergetic strategy of facet and vacancy engineering for the construction of highly efficient heterogeneous catalyst BiO1-xBr1-y-(010) for CO2 cycloaddition, where introducing the OVs-BrVs pairs into typical (010) facets BiOBr with simultaneous surface Lewis acid sites Bi3+ and nucleophilic sites Br−. By combining theoretical calculations and a series of systematic experiments, such as CO2 temperature-programmed desorption, electron paramagnetic resonance and fluorescence probe analysis experiments, the introduced OVs-BrVs pair can not only form Bi3+-Bi(3-x)+ dual active sites on the surface, which activate PO and CO2 respectively to reduce the energy barrier of CO2 insertion, but also activate Br− near BrVs to enhance their nucleophilic attacking ability and reduce the energy barrier of epoxides ring-opening. As a result, the BiO1-xBr1-y-(010) with abundant surface OVs-BrVs pairs showed a high cyclic carbonates conversion of 99 % with 100 % selectivity under cocatalyst-free and mild conditions, far surpassing most heterogeneous catalytic systems. This work provides a completely new strategy to construct high-performance heterogeneous CO2 cycloaddition catalysts through a simple facet and vacancy engineering strategy to overcome the harsh operating conditions limitation and the use of cocatalysts.

Selective Hydrogenolysis of Furfuryl Alcohol to Pentanediol over Pt Supported on MgO

The catalytic conversion of naturally rich and renewable biomass into high-value chemicals is of great significance for pursuing a sustainable future and a green economy. The preparation of pentanediol from furfuryl alcohol is an important means of high-value conversion of biomass. The Pt-based catalyst supported on MgO was applied to the selective hydrogenation of biomass furfuryl alcohol to prepare pentanediol. By adjusting parameters such as catalyst loading, reduction temperature, reaction temperature, and pressure, a highly active catalyst was designed and the optimal catalytic hydrogenation conditions were determined. The hydrogenation experiment results showed that the selectivity of the 2Pt/MgO-200 catalyst for 1,2-pentanediol and 1,5-pentanediol reached 59.4% and 15.2%, respectively, under 160 °C and 1 MPa hydrogen pressure. The catalyst was characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectrometer (XPS), CO2-temperature programmed desorption (CO2-TPD), and other methods. The characterization results indicate that the reduction temperature has a significant impact on the metal Pt, and an appropriate reduction temperature is beneficial for the hydrogenation performance of the catalyst. In addition, the basic sites on the carrier are also another important factor affecting the activity of the catalyst. In addition, stability tests were conducted on the catalyst, and the reasons for catalyst deactivation were studied using methods such as thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). The results showed that the activity of the catalyst decreased after five cycles, and the deactivation was due to the hydrolysis of the carrier, the increase in metal particle size, and the surface adsorption of organic matter.

Cs-promoted hydrogenation upgrading of bio-oil over macroporous Ru-containing catalysts using model compounds

Hydrogenation upgrading is an effective technique that lowers the oxygen content of bio-oil with the aim of improving its quality. In order to fabricate a series of Ru-based catalysts for the hydrodeoxygenation of bio-oil, several all-silica supports with different pore sizes are synthesized and modified with Al and Cs in this work. The physical morphology and electronic structure of the catalysts are characterized using multiple techniques including X-ray diffraction, in-situ pyridine adsorption infrared spectroscopy, in-situ diffuse reflectance Fourier transform infrared spectroscopy, Raman spectroscopy, CO2 temperature-programmed desorption, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and N2 physical adsorption-desorption testing. Phenol, guaiacol, anisole and o-cresol are selected as model compounds to investigate the hydrodeoxygenation reactivity of the catalysts. The results reveal that there is a strong linear correlation between the pore size of the catalysts and the rates of the hydrogenation and hydrodeoxygenation of phenol. Importantly, both the oxygen vacancy density and relative content of Brønsted and Lewis sites (B/L) of the catalysts can be greatly increased by Cs modification, which further linearly promotes the hydrodeoxygenation activity of the catalysts. In addition, the in-situ infrared spectroscopy results show that the catalysts modified by Al and Cs heterolytically cleave H2 to supply H+ for the reaction. This work presents a novel approach for fabricating catalysts employed in the hydrotreatment process of bio-oil.

Assessing the effect of acid and alkali treatment on a halloysite-based catalyst for dry reforming of methane.

Dry reforming of methane (DRM) has recently received wide attention owing to its outstanding performance in the reduction and conversion of CH4 and CO2 to syngas (H2 and CO). From an industrial perspective, nickel (Ni)-supported catalysts have been deemed among the most suitable catalysts for DRM owing to their low cost and high activity compared to noble metals. However, a downside of nickel catalysts is their high susceptibility to deactivation due to coke formation and sintering at high temperatures. Using appropriate supports and preparation methods plays a major role in improving the activity and stability of Ni-supported catalysts. Halloysite nanotubes (HNTs) are largely utilized in catalysis as a support for Ni owing to their abundance, low cost, and ease of preparation. The treatment of HNTs (chemical or physical) prior to doping with Ni is considered a suitable method for increasing the overall performance of the catalyst. In this study, the surface of HNTs was activated with acids (HNO3 and H2SO4) and alkalis (NaOH and Na2CO3 + NaNO3) prior to Ni doping to assess the effects of support treatment on the stability, activity, and longevity of the catalyst. Nickel catalysts on raw HNT, acid-treated HNT, and alkali-treated HNT supports were prepared via wet impregnation. A detailed characterization of the catalysts was conducted using X-ray diffraction (XRD), BET surface area analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), solid-state nuclear magnetic resonance (ssNMR), H2-temperature programmed reduction, (H2-TPR), CO2-temperature programmed desorption (CO2-TPD), and Ni-dispersion via H2-pulse chemisorption. Our results reveal a clear alteration in the structure of HNTs after treatment, while elemental mapping shows a uniform distribution of Ni throughout all the different supports. Moreover, the supports treated with a molten salt method resulted in the overall highest CO2 and CH4 conversion among the studied catalysts and exhibited high stability over 24 hours testing.

Characterization of CO Adsorbed to Clean and Partially Oxidized Cu(211) and Cu(111).

Copper-based catalysts gain activity through the presence of poorly coordinated Cu atoms and incomplete oxidation at the surface. The catalytic mechanisms can in principle be observed by controlled dosing of reactants to single-crystal substrates. However, the interconnected influences of surface defects, partial oxidation, and adsorbate coverage present a large matrix of conditions that have not been fully explored in the literature. We recently characterized oxygen and carbon monoxide coadsorption on Cu(111), a nominally defect-free surface, and now extend our study to the stepped surface Cu(211). Temperature-programmed desorption of CO adsorbed to bare metal surfaces confirms that two sites dominate desorption from a saturated layer: atop terrace atoms of local (111) character and atop step edge atoms with CO bound more strongly to the latter. At low coverage, discrete CO resonances in reflection adsorption infrared spectra can be assigned to these sites: 2077 cm-1 for extended (111) terraces, 2093 cm-1 for step sites, and additional kink-adsorbed molecules at 2110 cm-1. With increasing coverage, in contrast to Cu(111), the infrared spectral features on Cu(211) evolve and shift as a consequence of dipole-dipole coupling between differentially occupied types of sites. Auger electron spectroscopy shows that exposure to background O2 oxidizes the (211) surface at a rate nearly 1 order of magnitude greater than (111); we argue that the resulting surface is stoichiometric Cu2O, as previously found for Cu(111). This oxide binds CO less strongly than the bare metal and the underlying crystal cut continues to influence the adsorption sites available to CO. On oxidized (111) terraces, broad absorption peaks at 2115-2120 cm-1; on oxidized Cu(211), CO adsorbed to step sites appears as a resolved secondary peak at 2144 cm-1. This suite of spectroscopic signatures, obtained under carefully controlled conditions, will help to determine the origin and fate of adsorbed species in future studies of reaction mechanisms on copper.

BaTiO3-xNy: Highly Basic Oxide Catalyst Exhibiting Coupling of Electrons at Oxygen Vacancies with Substituted Nitride Ions.

The base strength of oxide catalysts is controlled by the electron charge distribution between cations and anions, with unsaturated oxygen ions that have lone pair electrons typically acting as basic sites. Substitution of oxide ions with anions that have different valences, such as nitride and hydride ions, can often generate basic sites. It is plausible that electrons trapped at oxygen vacancy sites could provide increased electron density and shift the highest occupied molecular orbital energy levels of anions upward in the case that the oxygen vacancies couple with surface-substituted anions. The present work demonstrates that high catalytic basicity can be obtained via site-selective doping of anions at face-sharing Ti2O9 dimer sites with oxygen vacancies in BaTiO3-x. This improved basicity stems from the coupling of substituted nitride ions to electrons at oxygen vacancies. The oxynitride BaTiO3-xNy was found to contain nitride ions that have increased electronic charge density on the basis of such interactions. Enhanced surface basicity following doping with nitride ion was also confirmed by CO2 temperature-programmed desorption and infrared spectroscopy in conjunction with the adsorption of CHCl3. The strong Lewis base sites resulting from the formation of the oxynitride evidently facilitated the catalytic activation of C-H bonds to promote Knoevenagel condensation reactions between aldehydes and active methylene compounds with pKa values of up to 28.9.

Effect of Support on Oxidative Esterification of 2,5-Furandiformaldehyde to Dimethyl Furan-2,5-dicarboxylate

One-step oxidative esterification of 2,5-furandiformaldehyde (DFF) derived from biomass to prepare Dimethyl Furan-2,5-dicarboxylate (FDMC) not only simplifies the catalytic process and increases the purity of the product, but also avoids the polymerization of 5-hydroxymethylfurfural (HMF) at high-temperature conditions. Gold supported on a series of acidic oxide, alkaline oxide, and hydrotalcite was prepared using colloidal deposition to explore the effect of support on the catalytic activities. The Au/Mg3Al-HT exhibited the best catalytic activity, with 97.8% selectivity of FDMC at 99.9% conversion of DFF. This catalyst is also suitable for oxidative esterification of benzaldehyde and furfural. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and CO2 temperature programmed desorption (CO2-TPD) were performed to characterize the catalysts. The results indicated that the medium and strong basic sites in the catalysts benefited for the absorption of intermediate agents and facilitated the oxidative esterification of aldehyde groups, while neutral or acidic supports tended to produce an acetal reaction. It is worth noting that basicity on the support surface reduced the electronic state of the Au nanoparticle (Auδ−) and, thus, enhanced the catalytic selectivity of oxidative esterification. This finding demonstrated that the support plays a crucial role in oxidative esterification.

CeO2 nanorods supported CuOx-RuOx bimetallic catalysts for low temperature CO oxidation

Bimetallic catalysts often outperform monometallic catalysts due to changeable structural orientation, synergistic effects, and integration of two different metal or metal oxide properties. Here, a series of CeO2 nanorods (NR) supported bimetallic CuOx and RuOx catalysts (Cu: Ru ratios of 9:1, 7:3, and 5:5) were prepared using a wet impregnation method. In situ DRIFTS, H2 temperature programmed reduction (H2-TPR), CO temperature programmed desorption (CO-TPD), and other characterization techniques were used to investigate the effect of the Cu:Ru ratio on the activity of low-temperature CO oxidation. Among three catalysts, CeO2 NR supported 7 wt% Cu-3 wt% Ru catalyst after a reduction activation treatment showed the best performance with 100 % CO conversion at 166 °C and the lowest activation energy of 18.37 kJ mol−1. Raman and XPS profiles revealed that the origin of the superior performance is at least partially related to the high surface oxygen vacancy concentration and other distinct oxygen species (physi-/chemi-sorbed oxygen and bulk lattice oxygen), leading to outstanding adsorption and oxidation property of CO.

CO2-assisted oxidative dehydrogenation of ethane to ethylene over the ZnO-ZrO2 catalyst

The ZnO-ZrO2 catalyst was prepared by the deposition-precipitation method using ZrO2 as the carrier obtained from calcining commercial zirconium hydroxide (Zr(OH)4). And the catalytic performance was evaluated at 873 K in CO2-assisted ethane oxidative dehydrogenation reaction (CO2-ODHE). The physical-chemical properties and morphology were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Raman spectra, High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectra (XPS), CO2 temperature-programmed desorption (CO2-TPD). The results show that ZnO were doped into the surface lattice of ZrO2 on the 5%ZnO-ZrO2 catalyst, generating highly dispersed ZnO species and oxygen-deficient regions on catalyst surface. 5%ZnO-ZrO2 catalyst could selectively breaking C–H bond instead of C–C bond, delivering excellent catalytic performance. 210 μmol/(gcat·min) of C2H4 formation rate could compare favorably with the data reported on noble metal and transition metal carbides. Additionally, the possible mechanism is discussed.

BCN materials with adjustable active sites as heterogeneous acid–base catalysts for Knoevenagel condensation reaction

The Knoevenagel condensation reaction is one of the most effective methods for the formation of C–C bonds. However, developing efficient heterogeneous catalysts for the Knoevenagel condensation reaction is imperative. In this study, a series of boron carbon nitride (BCN) catalysts with adjustable active sites were designed via molecular self-assembly and calcination-temperature adjustment. The BCN materials synthesized at a calcination temperature of 750 °C (BCN-750) had the largest number of active sites and exhibited excellent activity, with a yield of 96% in the condensation reaction of benzaldehyde and malononitrile in only 4 min at room temperature. The excellent catalytic activity was attributed to the B and N species at the B–N–C sites, which functioned as acids and bases, respectively, to catalyze the Knoevenagel condensation reaction. This result was confirmed by temperature-programmed desorption of CO2 (CO2 TPD), temperature-programmed desorption of NH3 (NH3 TPD), X-ray photoelectron spectroscopy (XPS), and 11B solid-state magic-angle spinning nuclear magnetic resonance spectroscopy. In addition, aromatic and aliphatic aldehydes were successfully converted into their corresponding products. Analysis of the catalytic mechanism revealed that the deprotonation of malononitrile to form a carbanion was the rate-determining step.

Transfer hydrogenation of furfural to furfuryl alcohol under microwave irradiation using mixed oxides.

The reaction to obtain furan alcohols is one of the most important in the upgrading of furan derivates. An attractive route is the transfer hydrogenation of furfural using acidic-basic catalysts. In this work, mixed oxides derived from ternary hydrotalcites were employed to obtain furfuryl alcohol from furfural assisted by microwave irradiation. The reaction was studied using containing Co2+ and Ni2+ in their structure and was then optimized using distinct primary and secondary alcohols as hydrogen donor sources, as well as distinct temperatures and initial concentrations of furfural. The yields to furfuryl alcohol are strongly dependent on the type of Me2+ in layered oxides mainly due to higher basicity and also to the donor employed in the reaction. The mixed oxide containing Co2+ showed complete conversion of furfural and higher yields to furfuryl alcohol (> 95%) at short times of reaction (< 1 h).

Glycerol conversion in the presence of ethanol over CoFe2O4/SBA-15 mesoporous catalyst: Effect of the co-reagent on the catalytic performance

The synthesis and characterization of cobalt ferrite supported on mesoporous SBA-15 was presented to act as a catalyst in the glycerol conversion reaction in the presence of ethanol. Characterizations via X-ray diffraction (XRD) and FTIR spectroscopy confirmed the syntheses of SBA-15 and the CoFe2O4 phase dispersed on porous silica. Raman spectroscopy showed the ferrite with a degree of inversion (δ) of 0.4. The redox property was evaluated by TPR-H2 which exhibited reduction events above 400 °C, referring to the reduction of Co2+ and Fe3+ species. N2 physisorption analysis showed a surface area of 372 m2/g and a total pore volume of 0.65 cm3/g, indicating the presence of oxide on the surface and in the mesochannels of the support. Scanning electron microscopy (SEM) confirmed maintenance of support morphology after the impregnation process, while transmission electron microscopy (TEM) showed an average particle size of 6 nm for the supported cobalt ferrite. TEM images also confirmed that the typical mesoporosity of SBA-15 was maintained after spinel insertion. The acid-base properties of the catalyst indicated the presence of weak basic sites by CO2 temperature-programmed desorption (TPD-CO2) and the presence of Lewis acid sites by NO and Pyridine adsorption followed by FTIR analysis. The catalytic tests showed greater performance for the conversion glycerol in the presence of ethanol as co-reagent, considering that ethanol favors the interaction of glycerol with the solid surface and benefits the catalytic cycle. The reaction showed a conversion of only 20% in the absence of ethanol, while in the presence of the cosolvent a conversion greater than 80% was observed.

Preparation of Ce-MnOx Composite Oxides via Coprecipitation and Their Catalytic Performance for CO Oxidation.

Ce-MnOx composite oxide catalysts with different proportions were prepared using the coprecipitation method, and the CO-removal ability of the catalysts with the tested temperature range of 60-140 °C was investigated systematically. The effect of Ce and Mn ratios on the catalytic oxidation performance of CO was investigated using X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), H2 temperature programmed reduction (H2-TPR), CO-temperature programmed desorption (CO-TPD), and in situ infrared spectra. The experimental results reveal that under the same test conditions, the CO conversion rate of pure Mn3O4 reaches 95.4% at 170 °C. Additionally, at 140 °C, the Ce-MnOx series composite oxide catalyst converts CO at a rate of over 96%, outperforming single-phase Mn3O4 in terms of catalytic performance. With the decrement in Ce content, the performance of Ce-MnOx series composite oxide catalysts first increase and then decrease. The Ce MnOx catalyst behaves best when Ce:Mn = 1:1, with a CO conversion rate of 99.96% at 140 °C and 91.98% at 100 °C.

Promotion effects of alkali metals on iron molybdate catalysts for CO2 catalytic hydrogenation

CO2 hydrogenation is an attractive way to store and utilize carbon dioxide generated by industrial processes, as well as to produce valuable chemicals from renewable and abundant resources. Iron catalysts are commonly used for the hydrogenation of carbon oxides to hydrocarbons. Iron-molybdenum catalysts have found numerous applications in catalysis, but have been never evaluated in the CO2 hydrogenation. In this work, the structural properties of iron-molybdenum catalysts without and with a promoting alkali metal (Li, Na, K, Rb, or Cs) were characterized using X-ray diffraction, hydrogen temperature-programmed reduction, CO2 temperature-programmed desorption, in-situ 57Fe Mossbauer spectroscopy and operando X-ray adsorption spectroscopy. Their catalytic performance was evaluated in the CO2 hydrogenation. During the reaction conditions, the catalysts undergo the formation of an iron (II) molybdate structure, accompanied by a partial reduction of molybdenum and carbidization of iron. The rate of CO2 conversion and product selectivity strongly depend on the promoting alkali metals, and electronegativity was identified as an important factor affecting the catalytic performance. Higher CO2 conversion rates were observed with the promoters having higher electronegativity, while low electronegativity of alkali metals favors higher light olefin selectivity.

Steel Slag Decorated with Calcium Oxide and Cerium Oxide as a Solid Base for Effective Transesterification of Palm Oil

For further resource utilization of solid waste steel slag and the reduction in biodiesel production costs, this study used steel slag as a carrier to synthesize a CaO-CeO2/slag solid base catalyst for the effective transesterification of palm oil into fatty acid methyl esters (FAMEs). The synthesis involved a two-step impregnation of steel slag with nitrate of calcium and cerium and thermal activation at 800 °C for 180 min. Then, the catalysts’ textural, chemical, and CO2 temperature-programmed desorption properties were characterized. The catalytic activity depended highly on the ratio of Ca-Ce to steel slag mass; the CaO-CeO2/slag-0.8 catalyst showed outstanding performance. Characterization showed that the surface area and total basicity of the Ca-Ce/slag-0.8 catalyst were 3.66 m2/g and 1.289 mmol/g, respectively. The reactivity results showed that FAMEs obtained using 7 wt.% catalyst, 9:1 of methanol-to-palm-oil molar ratio, 180 min reaction duration, and 70 °C reaction temperature was optimum (i.e., 95.3% yield). In addition, the CaO-CeO2/slag-0.8 catalyst could be reused for at least three cycles, retaining 91.2% of FAMEs yield after n-hexane washing. Hence, the catalyst exhibits an excellent potential for cost-effective and environmentally friendly biodiesel production.