Surface Basicity Of Catalysts Research Articles

Rare earth oxide promoted Ru/Al2O3 dual function materials for CO2 capture and methanation: An operando DRIFTS and TGA study

Dual-function materials (DFMs) combine sorbent and catalytic components to perform selective CO2 capture and subsequent hydrogenation. This study explores the performance of rare-earth oxides (REOs) as CO2 adsorption sites on Ru/Al2O3. REOs increase CO2 uptake by upwards of +60 % by enhancing the overall catalyst surface basicity and favoring metal–support interactions. Thermogravimetric analysis during CO2 adsorption-hydrogenation cycles exhibited significant catalytic activity and enhanced stability of Ru-REO/Al2O3 at temperatures as low as 200 °C. This leads to methane production of 50–85 µmol g−1, surpassing recently reported values obtained for alkali and alkali-earth promoted Ru-based materials operated at 250 °C. The highest performing studied DFM, RuNd2O3/Al2O3, achieved 85 % CO2 capture efficiency and steadily produced methane in cyclic operation (+120 % CO2 uptake relative to Ru/Al2O3). Operando DRIFTS revealed that the dominant mechanism for methane formation is the hydrogenation of ruthenium carbonyls, which are stabilized by REOs. Upon CO2 exposure, surface carbonates and bicarbonate species form more abundantly on DFMs than on Ru/Al2O3. This confirms that REOs enhance the adsorption and retention of carbonates, which generate additional promoter-related reaction pathways during low-temperature hydrogenation. These findings are crucial in the advancement of sustainable, wider operation range carbon capture and utilization technologies.

Cu supported Fe-SiO2 nanocomposites for reverse water gas shift reaction

This work analyses the catalytic activity displayed by Cu/SiO2, Cu-Fe/SiO2 and Cu/FSN (Fe-SiO2 nanocomposite) catalysts for the Reverse Water Gas Shift reaction. Compared to Cu/SiO2 catalyst, the presence of Fe resulted on higher CO’s selectivity and boosted resistances against the constitution of the deactivation carbonaceous species. Regarding the catalytic performance however, the extent of improvement attained through incorporation Fe species strongly relied on the catalysts’ configuration. At 30 L/gh and H2:CO2 ratios = 3, the performance of the catalysts’ series increased according to the sequence: Cu/SiO2 < Cu-Fe/SiO2 << Cu/FSN. The remarkable catalytic enhancements provided by Fe-SiO2 nanocomposites under different RWGS reaction atmospheres were associated to enhanced catalyst surface basicity’s and stronger Cu-support interactions. The catalytic promotion achieved by Fe-SiO2 nanocomposites argue an optimistic prospective for nanocomposite catalysts within future CO2-valorising technologies.

Effect of Basicity on Cu Based Catalyst for CO2 Hydrogenation

The purpose of this research is to study the effect of the MgO loading (0.25, 0.5, 1 and 2 Molar) on the Cu/AC catalysts for CO2 hydrogenation. The optimum condition of reaction temperature and ratio of H2:CO2 for CO2 hydrogenation were also investigated. Copper based catalysts were characterized by BET, CO2-TPD, H2-TPR and CO2-TPSR. The catalytic performance of catalysts were carried out in the fixed bed reactor at a reaction temperature of 250 °C pressure of 1 atm with mixture gas of 2:1 molar ratio of H2:CO2. The result shows that MgO increases the surface basicity of catalyst which enhances the bond strength between CO adsorbed on Cu loading to inhibition the reverse water-gas shift reaction, which can well promote the methane selectivity. The optimum conditions for CO2 hydrogenation is temperature of reaction at 300 °C and ratio of H2:CO2 as 2:1.

Methane decomposition over Fe-based catalysts

Catalytic approach for methane decomposition can be seriously considered as a promising process for COx free hydrogen generation. In this study, catalytic methane decomposition was performed using Fe-based catalysts, and catalytic performance tests were carried out in a CH4:N2 flow at 750 and 800 °C. The analyses of reaction products were carried out by a mass spectrometer. For the preparation of Fe-based catalysts, sol-gel method was utilized. Yttria (Y2O3) and alumina (Al2O3) were used as support materials. Theoretical molar ratios (Fe2O3/Y2O3/Al2O3) of the samples C1–C5 were 1:0:0, 1:1:0, 1:1:5, 2:1:4 and 3:1:6, respectively. The characterization analyses of fresh and spent catalysts were performed with XRD, SEM, TPR, TG-FTIR and BET surface analysis techniques. Surface basicity of catalysts was determined via CO2-TPD measurements. In the presence of Fe2O3/Y2O3 and Fe2O3/Y2O3/Al2O3 catalysts, methane conversions of 29% and 4% were achieved at 750 °C. Adding alumina into Fe2O3/Y2O3 catalyst leads to the formation of garnet type crystal structure which reduces catalytic activity.

Cu/Fe3O4 catalyst for water gas shift reaction: Insight into the effect of Fe2+ and Fe3+ distribution in Fe3O4

Two precursors, namely, p-CFO-T (tetragonal) and p-CFO-C (cubic), were fabricated by a sol-gel method via citric acid and poly(vinyl alcohol) complexation, respectively. After H2-reduction, the two were converted to Cu/Fe3O4 catalysts of different complexions, which are named as CFO-CA and CFO-PVA, respectively. The distribution of Fe2+ and Fe3+ in the Cu/Fe3O4 catalysts was studied by Raman and XPS techniques. It was disclosed that the distribution of Fe2+ and Fe3+ in Fe3O4 has an effect on Cu–Fe3O4 interaction and catalyst surface basicity. Compared to CFO-PVA, CFO-CA has a larger amount of Fe3+, which mostly sits at the octahedral sites, leading to stronger Cu–Fe3O4 interaction, and a larger amount of catalyst surface sites that are of weak basicity. As a result, the critical elementary steps of WGS reaction, viz. water dissociation, –COOH decomposition and CO2 desorption are promoted as reflected in the lower Ea and higher catalytic activity of CFO-CA.

Effect of Li promoter on FeMn/CNTs for light olefins from syngas

FeMnLi/CNTs catalysts with different Li content were prepared by the incipient wetness impregnation method for light olefins from syngas and investigated by N2 adsorption-desorption, XRD, H2-TPR, CO2-TPD and Mӧssbauer techniques. The addition of Li increased the surface basicity of catalysts and promoted the transformation of Fe3+ specious and formation of active phase, χ-Fe5C2, which was favorable to CO conversion and light olefins selectivity. The best catalytic performance was achieved over 8Fe8Mn1.5Li catalyst with CO conversion of 14.18% and light olefins selectivity of 48.42%.

La/Zn Bimetallic Oxide Catalyst for Epoxidation of Styrene by Cumene Hydroperoxide: Kinetics and Reaction Engineering Aspects

Styrene oxide (STOX) is mostly produced by chlorohydrin process that generates large amount of waste. A greener alternative to the chlorohydrin process is epoxidation of styrene induced by hydroperoxides. In this work, we have studied this reaction using cumene hydroperoxide (CHP) as oxygen inducing reagent under the influence of the prepared La–Zn bimetallic oxides, which offered reasonably high catalytic activity in terms of conversion and high selectivity for styrene oxide. The side reactions can be suppressed by a proper choice of reaction conditions and mode of reaction. At a given reactant conversion, semibatch modes of operation exhibits higher styrene and CHP-based product selectivity when compared with its batch counterpart. Parametric studies are performed to examine the effects of temperature (ambient temperature 363 K), catalyst loading (0.25–1%), CHP-to-styrene mole ratio (∼1–3.5), presence of nonreacting solvent, and surface basicity of catalysts. Catalyst deactivation was studied in detail ...

Lysine-assisted synthesis of porous Ba-doped Pd/γ-Al2O3 hollow microspheres with enhanced catalytic properties for CO and C3H8 oxidation

Porous Ba-doped Pd/γ-Al2O3 hollow microspheres were successfully synthesized via a simple hydrothermal method with the assistance of lysine, barium and NH4HCO3. The introduction of lysine and NH4HCO3 is beneficial to the formation of porous hollow microspheres and the promotion of specific surface area. The addition of BaO effectively improves the surface basicity of catalysts. The obtained porous Pd/Ba-γ-Al2O3 hollow microspheres are about 5–6 μm in diameter and shell thickness of 1 μm. The porous Pd/Ba-γ-Al2O3 hollow microspheres also exhibit higher catalytic activity for CO and C3H8 oxidation compared with the one without adding lysine and NH4HCO3.

Efficient and versatile CuNi alloy nanocatalysts for the highly selective hydrogenation of furfural

The development of efficient and environmental benign non-noble bimetallic nanocatalysts is highly desirable and attractive in the upgrading of biomass-derived platform compounds to high-valued chemicals. A series of highly dispersed and versatile CuxNiy (x/y=7:1, 3:1, 1:1, 1:3, 1:7) alloy supported nanocatalysts derived from layer double hydroxides (LDHs) precursors were fabricated and used for the selective hydrogenation of furfural to tetrahydrofurfuryl alcohol (THFA) and furfuryl alcohol (FOL). It was found that the chemical composition, preparation method and especially the reduction temperature of LDHs precursors greatly affected the properties of the resultant CuxNiy/MgAlO catalysts. Systematic characterizations revealed that the reduction temperature of catalyst precursor was closely related to the dispersion and homogeneous composition of CuNi alloy nanoparticle as well as the surface basicity of catalysts, which played crucial roles in achieving excellent catalytic performances. The optimized CuNi/MgAlO and Cu1Ni3/MgAlO nanocatalysts showed high activity and selectivity for the hydrogenation of furfural to THFA in ethanol compared with the monometallic Ni and the CuNi supported catalysts prepared with other methods, such enhanced catalytic performance was investigated to be enabled by the synergistic effect within the CuNi alloy nanoparticles. Interestingly, our bimetallic nanocatalysts could also realize efficient production of FOL from the selective hydrogenation of furfural at its aldehyde group by simply changing the solvent to methanol. Moreover, the bimetallic nanocatalysts showed good recyclability in the liquid phase hydrogenation. Our efficient and versatile CuNi alloy nanocatalysts not only provide promising candidates for effective upgrading of furfural but also broaden the application of non-noble bimetallic nanocatalysts for hydrogenative transformations.

Methanol synthesis from CO2 hydrogenation over copper catalysts supported on MgO-modified TiO2

A serials of copper catalysts supported on TiO2 modified with different amount of MgO were prepared by an impregnation method and tested for methanol synthesis from CO2 hydrogenation. The physico-chemical properties of the catalysts were characterized using XRD, N2 physisorption, N2O titration, XPS, H2-TPR and CO2-TPD techniques. With the increase in amount of MgO, the Cu surface area initially increases and then decreases. The modification of TiO2 with MgO hinders the interaction between CuO and TiO2, resulting in a decline in the reducibility of CuO. Furthermore, the number and strength of the moderate and strong basic sites over the surface of catalyst increase with increasing MgO loading. The catalyst exhibits an optimum catalytic activity as the content of MgO is 1wt%. The CO2 conversion is determined by the Cu specific surface area and the interaction between CuO and TiO2, and the CH3OH selectivity is related to the surface basicity of catalyst.

Template-free synthesis of mesoporous γ-alumina-supported Ni–Mg oxides and their catalytic properties for prereforming liquefied petroleum gas

Mesoporous γ-alumina (γ-MA)-supported Ni–MgO catalysts were first prepared through one-pot hydrolysis of inorganic salts without surfactants and used for the prereformation of liquefied petroleum gas (LPG). The influence of MgO addition on catalyst structure, surface characteristics, distribution of Ni species, and reducibility of Ni2+ ions was investigated in detail. The prepared Ni–MgO/γ-MA catalysts possessed wormhole-like mesoporous structures with large surface areas, narrow pore size distributions, and metallic Ni nanoparticles f homogeneously dispersed in γ-MA frameworks. The results showed that MgO could improve catalyst surface basicity and lower metallic Ni particle sizes, resulting in significant enhancements in the activity, stability, and resistance to coke deposition for the prereformation of LPG. Comparative investigation of the prereformation of LPG over Ni–MgO/Al2O3 catalysts obtained by different routes revealed that the high stability and coke resistance ability were mainly due to the formation of smaller metallic Ni nanoparticles and stable support structures.

Preparation and characterization of nonmetal promoter modified CuZnAl catalysts for higher alcohol from synthesis gas through complete liquid phase method

A complete liquid phase technology and a function regulator were applied to prepare CuZnAl catalysts for higher alcohol synthesis. Characterizations showed that the introduction of the function regulator can change the reduction ability of copper oxides and the surface basicity of catalysts. Activity tests indicated that the selectivity of higher alcohol is high when considerable medium-strong basicity and the synergistic effects of copper ion and metal copper exist on the catalytic surface. The optimized modified CuZnAl catalyst without any metal additives provides a CO conversion of 28.9%, C2+OH selectivity of up to 42.8%, and hydrocarbon selectivity of 2.5%, with a total alcohol selectivity of 67.4% under the reaction conditions of 5.0 MPa, 250 °C, H2/CO = 1, and a gas hourly space velocity of 360 mL/gcat h.

Effect of manganese on the catalytic performance of an iron-manganese bimetallic catalyst for light olefin synthesis

A systematic study was carried out to investigate the promotion effect of manganese on the performance of a coprecipitated iron-manganese bimetallic catalyst for the light olefins synthesis from syngas. The catalyst samples were characterized by N2 physisorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), Mössbauer spectroscopy, H2-differential thermogravimetric analysis (H2-DTG), CO temperature-programmed reduction (CO-TPR) and CO2 temperature-programmed desorption (CO2-TPD). The Fischer-Tropsch synthesis (FTS) performance of the catalyst was measured at 1.5 MPa, 250 °C and syngas with H2/CO ratio of 2.0. The characterization results indicated that the addition of manganese decreases the catalyst crystallite size, and improves the catalyst BET surface area and pore volume. The presence of manganese suppresses the catalyst reduction and carburization in H2, CO and syngas, respectively. The addition of manganese improves the catalytic activity of water-gas shift reaction and suppresses the oxidation of iron carbides in the FTS reaction. The incorporation of manganese improves the catalyst surface basicity and results in a significant improvement in the selectivities to light olefins and heavy hydrocarbons (C5+), and furthermore an inhibition of methane formation in FTS. The pure iron catalyst (Mn-00) has the highest initial FTS catalytic activity (65%) and the lowest selectivity (17.35 wt%) to light olefins (C=2−C=4). The addition of an appropriate amount of manganese can improve the catalyst FTS activity.

Kinetic studies of the Fischer–Tropsch synthesis over La, Mg and Ca promoted nano-structured iron catalyst

The kinetic of the Fischer–Tropsch synthesis (FTS) over nano-structured iron catalyst promoted with Mg, La and Ca, was studied in a continuous spinning basket reactor. Fe/Cu/Si nano-structured catalyst was prepared by co-precipitation in a water-in-oil microemulsion. The results indicated that both the rate constant ( k) and the adsorption parameter ( b) in a common two-parameter Fischer–Tropsch rate expression decreased with increasing the catalyst surface basicity. Since decreases in rate constant ( k) and the adsorption parameter ( b) affected the FTS rate in reverse direction, the basicity of catalyst surface showed complicated effects on kinetic parameters of FTS reaction. The optimum promoter would be one that its rate constant ( k) should not be too low and its adsorption parameter ( b) should not be too high.

Studies on product distribution of alkali promoted iron catalyst in Fischer-Tropsch synthesis

The dependencies of hydrocarbon product distributions of alkali promoted iron catalyst in Fischer-Tropsch synthesis have been studied. The concept of two superimposed Anderson-Schulz-Flory distributions has been applied for the representation of the effects of Mg, La and Ca promoters on product distributions. The FTS performance of the catalysts was tested in a fixed bed reactor under the conditions 563 K, 1.7 MPa, H 2/CO = 1 and space velocities 4.86 and 13.28 nl·h −1·g Fe −1. The results indicate that appropriate amounts of these promoters enhance the break in ASF distributions in the order Ca > Mg > La because of the rising of the catalyst surface basicity.

Effect of Mg, La and Ca promoters on the structure and catalytic behavior of iron-based catalysts in Fischer–Tropsch synthesis

Abstract The effects of Mg, La and Ca promoters on the structure, surface area, reduction, carburization and catalytic behavior of precipitated Fe/Cu/SiO2 Fischer–Tropsch synthesis (FTS) catalysts were investigated. The catalysts are characterized using X-ray diffraction (XRD), H2 and CO temperature-programmed reduction (TPR) techniques. The catalysts were assessed in terms of their FTS activity and product selectivity using two superimposed Anderson–Schulz–Flory (ASF) models. The performance of the catalysts was tested in a fixed-bed reactor at 563 K, 1.7 MPa and feed (syngas with H2/CO molar ratio of 1) flow rates of 4.9 and 13.3 nl h−1 g(Fe)−1. It was found that Mg, La and Ca promoters have negligible effects on the textural properties of the catalyst. Promoter addition enhanced the surface basicity of the catalyst in the order Ca > Mg > La. Addition of the promoters with the atomic ratio of X/Fe = 0.02 (X = Ca, Mg and La) improved the reduction and carburization during the reduction and FTS reaction in the order of Ca > Mg > La. The promoters suppressed the rate of hydrogenation reaction in the order of Ca > Mg > La. The results also indicate that Mg, La and Ca promoters can improve the CO conversion and WGS reaction, suppress the formation of methane, enhance the selectivities to olefin and higher molecular weight products, enhance the break in ASF distributions in the order of Ca > Mg > La due to increasing the catalyst surface basicity and dropping the reducibility.

Effect of Sulfate on an Iron Manganese Catalyst for Fischer-Tropsch Synthesis

The effect of sulfate on Fischer-Tropsch synthesis performance was investigated in a slurry- phase continuously stirred tank reactor (CSTR) over a Fe-Mn catalyst. The physiochemical properties of the catalyst impregnated with different levels of sulfate were characterized by N 2 physisorption, X-ray photoelectron spectroscopy (XPS), H 2 (or CO) temperature-programmed reduction (TPR), Møssbauer spectroscopy, and CO 2 temperature-programmed desorption (TPD). The characterization results indicated that the impregnated sulfate slightly decreased the BET surface area and pore volume of the catalyst, suppressed the catalyst reduction and carburization in CO and syngas, and decreased the catalyst surface basicity. At the same time, the addition of small amounts of sulfate improved the activities of Fischer- Tropsch synthesis (FTS) and water gas shift (WGS), shifted the product to light hydrocarbons (C 1–C 11) and suppressed the formation of heavy products (C 12+). Addition of SO 2 − 4 to the catalyst improved the FTS activity at a sulfur loading of 0.05–0.80 g per 100 g Fe, and S-05 catalyst gave the highest CO conversion (62.3%), and beyond this sulfur level the activity of the catalyst decreased.

Promotional effect of Y 2O 3 on the performance of Ag/α-Al 2O 3 catalyst for epoxidation of propylene with molecular oxygen

The Ag/α-Al 2O 3 catalysts modified with rare earth, alkali and alkaline earth metal oxides for the epoxidation of propylene by molecular oxygen were prepared and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), CO 2-temperature programmed desorption (CO 2-TPD), BET surface area and pore diameter distribution. The results show that the appropriate pore diameter and high surface area of α-Al 2O 3 support, and the suitable basic sites on the surface of catalyst are necessary to the highly effective Ag catalyst for the epoxidation of propylene. The presence of a small quantity of Y 2O 3 can restrain the sintering of Ag particles on the surface of α-Al 2O 3 and adjust the surface basicity of catalyst. The loadings of promoters and reaction temperature obviously affect the performance of Ag catalysts. Under the reaction condition of 0.1 MPa, 245 °C, space velocity 2000 h −1 and the feed of 20% C 3H 6/8% O 2/N 2, 4% conversion of propylene and 46.8% selectivity to propylene oxide were obtained over the 20 wt% Ag–0.1% Y 2O 3–0.1% K 2O/α-Al 2O 3 catalyst.

IR study of adsorption and reaction of methylbutynol on the surface of pure and modified MgO catalysts: probing the catalyst surface basicity

FT infrared spectroscopy (FTIR spectroscopy) has been used to study the adsorption and reactivity of 2-methyl-3-butyn-2-ol (MBOH) on the surfaces of pure and Cs +- and Ba 2+-modified MgO. It has been found that MBOH is adsorbed via two different mechanisms. Dissociative adsorption at acid–base (M–O) pair-sites with the creation of new H-bonded surface OH s groups is the most favorable adsorption mode in the case of Cs/MgO. This is attributed to the strong Lewis basic sites generated on the catalyst surface upon impregnation with Cs + cations which facilitate abstraction of hydrogen from MBOH, leading to the formation of alcoholate species. On the other hand, the Ba/MgO catalyst adsorbs MBOH preferentially via interaction with surface hydroxyl groups. Both these adsorption modes are operative on the surface of pure MgO. The acetylenic group is also involved in the adsorption of MBOH. The acidic acetylenic hydrogen interacts with the Lewis basic sites, whereas the Lewis acid sites interact preferably with the acetylenic π-electron system. With regard to surface reactivity, the catalysts are active towards the decomposition of MBOH to acetone and acetylene, revealing their basic properties. The Cs/MgO catalyst exhibits higher activity than MgO, which appears to be more active than catalysts impregnated with Ba 2+ ion. The formation of BaCO 3 (as detected by X-ray diffractometry (XRD)) on the MgO surface may be responsible for this lower activity. It has been found that the reaction product acetone is polymerized rapidly and adsorbed strongly on the surfaces of Ba/MgO. In conclusion, the basicity of this series of catalysts can be ranked as follows: Cs/ MgO> MgO> Ba/ MgO

99/03625 Three-phase flow characteristics in a direct coal liquefaction reactor: Idogawa, K. Hokkaido Kogyo Gijutsu Kenkyusho Hokoku, 1999, 72, 1–12. (In Japanese)

A systematic study was carried out to investigate the promotion effect of manganese on the performance of a coprecipitated iron-manganese bimetallic catalyst for the light olefins synthesis from syngas. The catalyst samples were characterized by N2 physisorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), Mössbauer spectroscopy, H2-differential thermogravimetric analysis (H2-DTG), CO temperature-programmed reduction (CO-TPR) and CO2 temperature-programmed desorption (CO2-TPD). The Fischer-Tropsch synthesis (FTS) performance of the catalyst was measured at 1.5 MPa, 250 °C and syngas with H2/CO ratio of 2.0. The characterization results indicated that the addition of manganese decreases the catalyst crystallite size, and improves the catalyst BET surface area and pore volume. The presence of manganese suppresses the catalyst reduction and carburization in H2, CO and syngas, respectively. The addition of manganese improves the catalytic activity of water-gas shift reaction and suppresses the oxidation of iron carbides in the FTS reaction. The incorporation of manganese improves the catalyst surface basicity and results in a significant improvement in the selectivities to light olefins and heavy hydrocarbons (C5+), and furthermore an inhibition of methane formation in FTS. The pure iron catalyst (Mn-00) has the highest initial FTS catalytic activity (65%) and the lowest selectivity (17.35 wt%) to light olefins (C=2−C=4). The addition of an appropriate amount of manganese can improve the catalyst FTS activity.