Investigation on the promotional role of Ga2O3 on the CuO–ZnO/HZSM-5 catalyst for CO2 hydrogenation

Dimethyl ether (DME) can be directly synthesized from carbon dioxide and hydrogen by mixing methanol synthesis catalysts and methanol dehydration catalysts. The activity and selectivity of the catalyst can be greatly affected by the promoter; herein, we presented a series of CuO–ZnO–Ga₂O₃/HZSM-5 hybrid catalysts, which were prepared by the coprecipitation method. The effect of the Ga₂O₃ content on the structure and performance of the Ga-promoted Cu–ZnO/HZSM-5 based catalysts was thoroughly investigated. The results showed that the addition of Ga₂O₃ significantly increased specific surface areas and Cu areas, decreased the size of Cu particles, maintained the proportion of Cu⁺/Cu⁰ on the surface of the catalyst, and strengthened the metal–support interaction, resulting in high catalytic performance.

The additive Ga₂O₃ improved the catalytic performance of CuO–ZnO/HZSM-5 catalysts for hydrogenation of CO₂ to DME.     

Copper–cobalt catalysts supported on mechanically mixed HZSM-5 and γ-Al2O3 for higher alcohols synthesis via carbon monoxide hydrogenation

Mechanically mixed γ-Al₂O₃ and HZSM-5 (Si/Al = 50) with different mass ratio were utilized as support for Cu–Co higher alcohol synthesis catalysts prepared through incipient wetness impregnation. The textural and structural properties were studied using Ar low temperature adsorption and desorption, H₂-temperature programmed reduction (H₂-TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and catalytic performance measurements. The results indicated that the mechanically mixed HZSM-5 and γ-Al₂O₃ supported copper–cobalt catalysts were superior to either γ-Al₂O₃ or HZSM-5 supported ones with the same metal loading. The results revealed that using HZSM-5 and γ-Al₂O₃ mechanically mixed benefited the dispersion of metallic phases and stronger synergetic functions between smaller nanoparticles containing copper and/or cobalt, which is essential for HAS from CO hydrogenation. Under working conditions of P = 5.0 MPa, T = 300 °C, V(H₂) : V(CO) : V(N₂) = 4 : 2 : 1 and GHSV = 7200 mL g⁻¹ h⁻¹, mechanically mixed HZSM-5 and γ-Al₂O₃ supported catalysts showed higher catalytic activity than those over single support. For CuCo catalysts upon support containing 50.0 wt% HZSM-5 and 50.0 wt% γ-Al₂O₃, the CO conversion was 21.3% and the C₂₊ alcohol selectivity was 41.8%.

CuCo bimetallic catalysts over the mixed supports showed smaller average particle size, better dispersion of cobalt and copper species, and good activity for higher alcohols synthesis.     

Study of resistance performance of Al2O3–ZnO–Y2O3 thermal control coating exposed to vacuum-ultraviolet irradiation

As deep space exploration moves farther and farther away, thermal control coating of the in-orbit spacecraft will suffer a serious vacuum-ultraviolet radiation environment, which seriously threatens the reliability of the spacecraft in orbit. Therefore, it is important to improve the vacuum-ultraviolet resistance performance of the thermal control coating. In this work, the inorganic Al₂O₃–ZnO–Y₂O₃ thermal control coating was in situ fabricated on a 6061 aluminum alloy surface by PEO technology, and its vacuum-ultraviolet resistance performance was investigated. The results show that the Al₂O₃–ZnO–Y₂O₃ thermal control coating has a good resistance performance to vacuum-ultraviolet radiation, which is mainly because the large extinction coefficients of the ZnO and Y₂O₃ materials in the ultraviolet band are conducive to improving the ultraviolet resistance performance. Furthermore, the life prediction model of the Al₂O₃–ZnO–Y₂O₃ thermal control coating shows that its Δα_s value first slightly increases and then tends to be stable with the increase of ultraviolet irradiation time from 0 ESH to 25 000 ESH, and the maximum variation of Δα_s is about 0.0536. This work provides a material basis and technical support for the thermal control system of spacecraft with long life and high reliability.

The Al₂O₃–ZnO–Y₂O₃ thermal control coating in situ fabricated by PEO technology, shows a good resistance performance to vacuum-ultraviolet radiation. Further, its life prediction model at vacuum-ultraviolet irradiation is preliminarily established.     

A new highly active La2O3–CuO–MgO catalyst for the synthesis of cumyl peroxide by catalytic oxidation

In this study, different magnesium, copper, lanthanide single metal, and composite multimetal oxide catalysts were prepared via the coprecipitation route for the aerobic oxidation of cumene into cumene hydroperoxide. All catalysts were characterized using several analytical techniques, including XRD, SEM, EDS, FT-IR, BET, CO₂-TPD, XPS, and TG-DTG. La₂O₃–CuO–MgO shows higher oxidation activity and yield than other catalysts. The results of XRD and SEM studies show that the copper and magnesium particles in the catalyst are smaller in size and have a distribution over a larger area due to the introduction of the lanthanum element. The CO₂-TPD results confirmed that the catalyst has more alkali density and alkali strength, which can excite active sites and prevent the decomposition of cumene hydroperoxide. XPS results show that due to the promotional effect of La₂O₃, there are more lattice and active oxygen species in the catalyst, which can effectively utilize the lattice defects under the strong interaction between metal oxides for rapid adsorption and activation, thus improving the oxidation performance. Besides, La₂O₃–CuO–MgO exhibits good stability and crystalline structure due to its high oxygen mobility inhibiting coking during the cycle stability test. Finally, the possible reaction pathway and promotional mechanism on La₂O₃–CuO–MgO in cumene oxidation are proposed. We expect this study to shed more light on the nature of the surface-active site(s) of La₂O₃–CuO–MgO catalyst for cumene oxidation and the development of heterogeneous catalysts with high activity in a wide range of applications.

The La₂O₃–CuO–MgO catalyst acts on the oxidation of cumene and shows excellent catalytic activity through the coordination of surface and interior.     

Reactive adsorption desulfurization of NiO and Ni0 over NiO/ZnO–Al2O3–SiO2 adsorbents: role of hydrogen pretreatment

Reactive adsorption desulfurization (RADS) of Fluidized Catalytically Cracked (FCC) gasoline on reduced and unreduced NiO/ZnO–Al₂O₃–SiO₂ adsorbents was studied. Various characterizations such as powder X-ray diffraction (XRD), H₂-temperature-programmed reduction (H₂-TPR), the H₂/O₂ pulse titration (HOPT), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) are used to evaluate the effects of hydrogen pretreatment of the adsorbents. XRD and HOPT results indicate that NiO is hard to be reduced to Ni⁰ under the conditions of RADS. H₂-TPR shows that NiO might be reduced to Ni⁰ at the temperature of 598 °C, much higher than the temperature of RADS. The Ni 2p_3/2 spectrum of Ni⁰ is not observed for the reduced adsorbent, but the main peak of Ni 2p_3/2 of NiS is found for the spent adsorbent. The unreduced NiO/ZnO–Al₂O₃–SiO₂ adsorbent performs a better desulfurization than the reduced adsorbent at the beginning of desulfurization process. NiO and Ni⁰ are assumed as the main active components and present a good desulfurization ability in RADS. Finally, a change in the RADS mechanism is presented and discussed.

A possible reaction mechanism of desulfurization on NiO/ZnO–Al₂O₃–SiO₂ is discussed.     

Effect of Ni/Co mass ratio and NiO–Co3O4 loading on catalytic performance of NiO–Co3O4/Nb2O5–TiO2 for direct synthesis of 2-propylheptanol from n-valeraldehyde

In the direct synthesis of 2-propylheptanol (2-PH) from n-valeraldehyde, a second-metal oxide component Co₃O₄ was introduced into NiO/Nb₂O₅–TiO₂ catalyst to assist in the reduction of NiO. In order to optimize the catalytic performance of NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst, the effects of the Ni/Co mass ratio and NiO–Co₃O₄ loading were investigated. A series of NiO–Co₃O₄/Nb₂O₅–TiO₂ catalysts with different Ni/Co mass ratios were prepared by the co-precipitation method and their catalytic performances were evaluated. The result showed that NiO–Co₃O₄/Nb₂O₅–TiO₂ with a Ni/Co mass ratio of 8/3 demonstrated the best catalytic performance because the number of d-band holes in this catalyst was nearly equal to the number of electrons transferred in hydrogenation reaction. Subsequently, the NiO–Co₃O₄/Nb₂O₅–TiO₂ catalysts with different Ni/Co mass ratios were characterized by XRD and XPS and the results indicated that both an interaction of Ni with Co and formation of a Ni–Co alloy were the main reasons for the reduction of NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst in the reaction process. A higher NiO–Co₃O₄ loading could increase the catalytic activity but too high a loading resulted in incomplete reduction of NiO–Co₃O₄ in the reaction process. Thus the NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst with a Ni/Co mass ratio of 8/3 and a NiO–Co₃O₄ loading of 14 wt% showed the best catalytic performance; a 2-PH selectivity of 80.4% was achieved with complete conversion of n-valeraldehyde. Furthermore, the NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst showed good stability. This was ascribed to the interaction of Ni with Co, the formation of the Ni–Co alloy and further reservation of both in the process of reuse.

NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst with a Ni/Co mass ratio of 8/3 and NiO–Co₃O₄ loading of 14% shows the best catalytic performance.     

Direct DME synthesis on CZZ/H-FER from variable CO2/CO syngas feeds

Catalyst systems for the conversion of synthesis gas, which are tolerant to fluctuating CO/CO₂ gas compositions, have great potential for process-technical applications, related to the expected changes in the supply of synthesis gas. Copper-based catalysts usually used in the synthesis of methanol play an important role in this context. We investigated the productivity characteristics for their application in direct dimethyl ether (DME) synthesis as a function of the CO₂/CO_x ratio over the complete range from 0 to 1. For this purpose, we compared an industrial Cu/ZnO/Al₂O₃ methanol catalyst with a self-developed Cu/ZnO/ZrO₂ catalyst prepared by a continuous coprecipitation approach. For DME synthesis, catalysts were combined with two commercial dehydration catalysts, H-FER 20 and γ-Al₂O₃, respectively. Using a standard testing procedure, we determined the productivity characteristics in a temperature range between 483 K and 523 K in a fixed bed reactor. The combination of Cu/ZnO/ZrO₂ and H-FER 20 provided the highest DME productivity with up to 1017 g_DME (kg_Cu h)⁻¹ at 523 K, 50 bar and 36 000 ml_N (g h)⁻¹ and achieved DME productivities higher than 689 g_DME (kg_Cu h)⁻¹ at all investigated CO₂/CO_x ratios under the mentioned conditions. With the use of Cu/ZnO/ZrO₂//H-FER 20 a promising operating range between CO₂/CO_x 0.47 and 0.8 was found where CO as well as CO₂ can be converted with high DME selectivity. First results on the long-term stability of the system Cu/ZnO/ZrO₂//H-FER 20 showed an overall reduction of 27.0% over 545 h time on stream and 14.6% between 200 h and 545 h under variable feed conditions with a consistently high DME selectivity.

Catalyst systems for the conversion of synthesis gas, which are tolerant to fluctuating CO/CO₂ gas compositions, have great potential for process-technical applications, related to the expected changes in the synthesis gas supply.     

Ni nanocatalysts supported on mesoporous Al2O3–CeO2 for CO2 methanation at low temperature

The selectivity and activity of a nickel catalyst for the hydrogenation of carbon dioxide to form methane at low temperatures could be enhanced by mesoporous Al₂O₃–CeO₂ synthesized through a one-pot sol–gel method. The performances of the as-prepared Ni/Al₂O₃–CeO₂ catalysts exceeded those of their single Al₂O₃ counterpart giving a conversion of 78% carbon dioxide with 100% selectivity for methane during 100 h testing, without any deactivation, at the low temperature of 320 °C. The influence of CeO₂ doping on the structure of the catalysts, the interactions between the mesoporous support and nickel species, and the reduction behaviors of Ni²⁺ ions were investigated in detail. In this work, the addition of CeO₂ to the composites increased the oxygen vacancies and active metallic nickel sites, and also decreased the size of the nickel particles, thus improving the low temperature catalytic activity and selectivity significantly.

The addition of CeO₂ to form Ni composite catalysts increased the oxygen vacancies and active metallic nickel sites thus improving the low temperature CO₂ methanation performance.     

Highly active Cu/ZnO–Al catalyst for methanol synthesis: effect of aging on its structure and activity

The influence of aging of precipitates on the physical and catalytic properties of a copper/zinc oxide-aluminium (Cu/ZnO–Al) catalyst with an optimized composition (low Al concentration, Cu/Zn/Al = 68/29/3) prepared using co-precipitation has been investigated in detail. The change in the structure of precipitates with aging (from amorphous zincian georgeite to crystalline zincian malachite) strongly influences the micro- and nano-structure (Cu and ZnO crystallite size, exposed copper surface area, Cu–ZnO interactions and stability of ZnO) of the final Cu/ZnO–Al catalysts obtained after calcination and reduction of the precipitates. The results of catalytic activity in methanol synthesis from syngas show the higher intrinsic activity of the catalysts derived from aged zincian malachite precipitates as consequence of the increase in the exposed copper surface area and the Cu–ZnO contacts. The stability of catalysts under the reaction conditions was also improved in the catalysts derived from precipitates aged after crystallization of malachite. The catalyst derived from the precipitate removed close to the point of crystallization of malachite shows very poor activity in the methanol synthesis as consequence of its segregated large Cu crystallites in low contact with ZnO derived from the absence of carbonate retention after calcination of the precipitate and the presence of sodium species after conventional washing which favour the strong sintering and crystallization of Cu during reduction.

The catalysts derived from precipitates aged after crystallization of zincian malachite show higher activity and stability     

A modified random network model for P2O5–Na2O–Al2O3–SiO2 glass studied by molecular dynamics simulations

We investigated the short- and medium-range structural features of sodium aluminosilicate glasses with various P₂O₅ (0–7 mol%) content and Al/Na ratios ranging from 0.667 to 2.000 by using molecular dynamics simulations. The local environment evolution of network former cations (Si, Al, P) and the extent of clustering behavior of modifiers (Na⁺) is determined through pair distribution function (PDF), total correlation function (TDF), coordination number (CN), Q_xⁿ distribution and oxygen speciation analysis. We show that Al–O–P and Si–O–Al linkage is preferred over other connections as compared to a random model and that Si–O–Si linkage is promoted by the P₂O₅ addition, which is related to structural heterogeneity and generates well-separated silicon-rich and aluminum–phosphorus-rich regions. Meanwhile, due to the relatively high propensity of Al to both Si and P, heterogeneity can be partly overcome with high Al content. A small amount of Si–O–P linkages have been detected at the interface of separated regions. Clustering of Na⁺ is also observed and intensified with the addition of P₂O₅. Based on the simulated structural information, a modified random network model for P₂O₅-bearing sodium aluminosilicate glass has been proposed, which could be useful to optimize the mobility of sodium ions and design novel functional glass compositions.

(A) A modified structural model proposed for P₂O₅-bearing sodium aluminosilicate glasses. (B) Degree of preferred connection (DPC) of different T–O–T network linkage for LAP, MAP and HAP glass compositions with various P₂O₅ content.     

Synthesis of a porous SiO2–H3BO3–V2O5–P2O5 glassy composite: structural and surface morphological behaviour for CO2 gas sensing applications

The present work mainly focuses on the fabrication of a porous glass 40SiO₂–35H₃BO₃–19V₂O₅–6P₂O₅via a melt-quenching technique. The structural, morphological, and sensing behaviour of the glass sample was investigated successfully. The calculated density and molar volume of the fabricated glass are 2.4813 ± 0.124 g cm⁻³ and 35.7660 ± 1.708 cm³ mol⁻¹. XRD, SEM and TEM analyses confirmed the amorphous nature of the glass. FTIR results revealed the O–H bond formations, which indicate that the presence of water molecules is probably due to the porous nature of the glass. Further, BET analysis confirmed the mesoporous nature of the glass sample with a mean pore diameter of 7 nm. The sensing response of the synthesized glass at 1000 ppm concentration of CO₂ was found to be 3.05 with a response time 22.6 s and recovery time 25.8 s. Hence, this porous glass can be easily synthesized, is affordable, and was found to be useful for CO₂ gas sensing applications.

The present work mainly focuses on the fabrication of a porous glass 40SiO₂–35H₃BO₃–19V₂O₅–6P₂O₅via a melt-quenching technique.     

Effect of unmelted lime on the element distribution behavior on a CaO–SiO2–MgO–Al2O3–FeO–CaF2(–Cr2O3) slag

In this study, a CaO–SiO₂–Al₂O₃–MgO–FeO–CaF₂(–Cr₂O₃) slag was chosen according to the compositions of the stainless steel slag for industrial production, and a CaO block was added to the molten slag after the synthetic slag was fully melted. The influences of unmelted lime on the distribution of elements and the structure of product layers at the lime/slag boundary, particularly the existing state of chromium oxide in the chromium-bearing stainless steel slag, were deeply discussed by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and FactSage 7.1. The experiment results indicated that when the unmelted lime existed in the CaO–SiO₂–Al₂O₃–MgO–FeO–CaF₂ slag system, two product layers of periclase (MgO) and dicalcium silicate (Ca₂SiO₄) at the boundary of the CaO block were formed. However, when the CaO block was added in the CaO–SiO₂–Al₂O₃–MgO–FeO–CaF₂–Cr₂O₃ stainless steel slag, besides MgO and Ca₂SiO₄ product layers, needle-shaped calcium chromite (CaCr₂O₄) was also precipitated around the CaO block. Moreover, a small amount of Cr dissolved in the periclase phase. Eh–pH diagrams showed that the CaCr₂O₄ and MgO phase unstably existed in a weak acid aqueous solution. Therefore, the existence of unmelted lime in the stainless steel slag could enhance the leachability of chromium.

The effect of unmelted lime on the distribution of elements and structure of product layers in CaO–SiO₂–MgO–Al₂O₃–FeO–CaF₂(–Cr₂O₂) stainless steel slag and the action of unmelted lime phase mechanism in experimental slags was conducted.     

Hydrodesulfurization of dibenzothiophene using Pd-promoted Co–Mo/Al2O3 and Ni–Mo/Al2O3 catalysts coupled with ionic liquids at ambient operating conditions

Sulfur compounds in fuel oils are a major source of atmospheric pollution. This study is focused on the hydrodesulfurization (HDS) of dibenzothiophene (DBT) via the coupled application of 0.5 wt% Pd-loaded Co–Mo/Al₂O₃ and Ni–Mo/Al₂O₃ catalysts with ionic liquids (ILs) at ambient temperature (120 °C) and pressure (1 MPa H₂). The enhanced HDS activity of the solid catalysts coupled with [BMIM]BF₄, [(CH₃)₄N]Cl, [EMIM]AlCl₄, and [(n-C₈H₁₇)(C₄H₉)₃P]Br was credited to the synergism between hydrogenation by the former and extractive desulfurization and better H₂ transport by the latter, which was confirmed by DFT simulation. The Pd-loaded catalysts ranked highest by activity i.e. Pd–Ni–Mo/Al₂O₃ > Pd–Co–Mo/Al₂O₃ > Ni–Mo/Al₂O₃ > Co–Mo/Al₂O₃. With mild experimental conditions of 1 MPa H₂ pressure and 120 °C temperature and an oil : IL ratio of 10 : 3.3, DBT conversion was enhanced from 21% (by blank Ni–Mo/Al₂O₃) to 70% by Pd–Ni–Mo/Al₂O₃ coupled with [(n-C₈H₁₇)(C₄H₉)₃P]Br. The interaction of polarizable delocalized bonds (in DBT) and van der Waals forces influenced the higher solubility in ILs and hence led to higher DBT conversion. The IL was recycled four times with minimal loss of activity. Fresh and spent catalysts were characterized by FESEM, ICP-MS, EDX, XRD, XPS and BET surface area techniques. GC-MS analysis revealed biphenyl as the major HDS product. This study presents a considerable advance to the classical HDS processes in terms of mild operating conditions, cost-effectiveness, and simplified mechanization, and hence can be envisaged as an alternative approach for fuel oil processing.

Synergistic application of ionic liquids with Pd loaded Co–Mo@Al₂O₃ and Ni–Mo@Al₂O₃ catalysts for efficient hydrodesulfurization of dibenzothiophene at ambient conditions.     

Effects of calcination temperatures on the structure–activity relationship of Ni–La/Al2O3 catalysts for syngas methanation

A series of Ni–La/Al₂O₃ catalysts for the syngas methanation reaction were prepared by a mechanochemical method and characterized by thermogravimetric analysis (TG-DTA), X-ray fluorescence (XRF), X-ray diffraction (XRD), N₂ adsorption–desorption, H₂ temperature-programmed reduction (H₂-TPR), and X-ray photoelectron spectroscopy (XPS). The calcination temperatures (350–700 °C) had significant impacts on the crystallite sizes and interactions between NiO and Al₂O₃. The catalyst calcined at 400 °C (cat-400) showed a 12.1% Ni dispersion degree and the maximum bound state of NiO (54%) through the Gaussian fitting of H₂-TPR. Cat-400 also achieved the highest CO conversion, CH₄ selectivity and yield. Cat-400 exhibited good stability and catalytic activity in a lifetime testing of 200 h. The deactivation of cat-400 was mainly caused by carbon deposition according to the data from XRD, TG-DTG and XPS.

Calcination temperature affects the existing types of NiO, and the influence of the three NiO types on the catalytic activity of samples is bound type ≫ free type > combined type.     

Self-supporting V2O5 nanofiber-based electrodes for magnesium–lithium-ion hybrid batteries

The increasing demand for high energy, sustainable and safer rechargeable electrochemical storage systems for portable devices and electric vehicles can be satisfied by the use of hybrid batteries. Hybrid batteries, such as magnesium–lithium-ion batteries (MLIBs), using a dual-salt electrolyte take advantage of both the fast Li⁺ intercalation kinetics of lithium-ion batteries (LIBs) and the dendrite-free anode reactions. Here we report the utilization of a binder-free and self-supporting V₂O₅ nanofiber-based cathode for MLIBs. The V₂O₅ cathode has a high operating voltage of ∼1.5 V vs. Mg/Mg²⁺ and achieves storage capacities of up to 386 mA h g⁻¹, accompanied by an energy density of 280 W h kg⁻¹. Additionally, a good cycling stability at 200 mA g⁻¹ over 500 cycles is reached. The structural integrity of the V₂O₅ cathode is preserved upon cycling. This work demonstrates the suitability of the V₂O₅ cathode for MLIBs to overcome the limitations of LIBs and MIBs and to meet the future demands of advanced electrochemical storage systems.

This work shows the feasibility of a self-supporting V₂O₅ nanofiber-based cathode for magnesium–lithium-ion batteries reaching an energy density of 280 W h kg⁻¹.     

The site pair matching of a tandem Au/CuO–CuO nanocatalyst for promoting the selective electrolysis of CO2 to C2 products

Tandem catalysis, in which a CO₂-to-C₂ process is divided into a CO₂-to-CO/*CO step and a CO/*CO-to-C₂ step, is promising for enhancing the C₂ product selectivity when using Cu-based electrochemical CO₂ reduction catalysts. In this work, a nanoporous hollow Au/CuO–CuO tandem catalyst was used for catalyzing the eCO₂RR, which exhibited a C₂ product FE of 52.8% at −1.0 V vs. RHE and a C₂ product partial current density of 78.77 mA cm⁻² at −1.5 V vs. RHE. In addition, the C₂ product FE stably remained at over 40% over a wide potential range, from −1.0 V to −1.5 V. This superior performance was attributed to good matching in terms of the optimal working potential and charge-transfer resistance between CO/*CO-production sites (Au/CuO) and CO/*CO-reduction sites (CuO). This site pair matching effect ensured sufficient supplies of CO/*CO and electrons at CuO sites at the working potentials, thus dramatically enhancing the formation rate of C₂ products.

C₂ product FE of 52.8% was achieved in eCO₂RR at −1.0 V vs. RHE using a nanoporous hollow Au/CuO–CuO tandem catalyst due to the matching of optimal working potentials and charge-transfer resistances of the CO-production sites and CO-reduction sites.     

Dehydrocyclization–cracking of methyl oleate by Pt catalysts supported on a ZnZSM-5–Al2O3 hierarchical composite

The dehydrocyclization–cracking of methyl oleate was performed by ZnZSM-5–Al₂O₃ hierarchical composite-supported Pt catalysts in the range of 450–550 °C under 0.5 MPa hydrogen pressure. Most catalysts converted methyl oleate completely and produced aromatics with more than 10 wt% yield as well as valuable fuels even at 450 °C. The reactivity of catalysts changed remarkably depending on the addition method of Pt, while supporting Pt of 0–0.16 wt% did not affect the pore structure of each catalyst. When Pt was introduced into the composite support by the conventional impregnation method, remarkable hydrocracking proceeded through the decarboxylation and decarbonylation of methyl oleate and the successive conversion of C17 fragments and gave the significant amounts of gaseous products. Nevertheless, the selectivity for the aromatics of the gasoline fraction was relatively high and the yields of aromatics reached maximum 19% at 500 °C under 0.5 MPa, suggesting that gaseous olefins would be cyclized through the Diels–Alder reaction on ZnZSM-5 in the composite support. In contrast, when Pt was introduced into catalysts by ion-exchange with ZnZSM-5, the significant conversion of methyl oleate was inhibited and produced liquid fuels in a wide range.

The ideal reaction route in the dehydrocyclization–cracking of methyl oleate catalyzed by Pt/ZnZSM-5–Al₂O₃ is to produce xylene, toluene, and hydrogen through decarboxylation.     

Photocatalytic activity of Ag/Al2O3–Gd2O3 photocatalysts prepared by the sol–gel method in the degradation of 4-chlorophenol

The photocatalytic activity in the degradation of 4-chlorophenol (4-ClPh) in aqueous medium (80 ppm) using 2.0 wt% Ag/Al₂O₃–Gd₂O₃ (Ag/Al–Gd-x; where x = 2.0, 5.0, 15.0, 25.0 and 50.0 wt% of Gd₂O₃) photocatalysts prepared by the sol–gel method was studied under UV light irradiation. The photocatalysts were characterized by N₂ physisorption, X-ray diffraction, SEM, HRTEM, UV-Vis, XPS, FTIR and fluorescence spectroscopy. About 67.0% of 4-ClPh was photoconverted after 4 h of UV light irradiation using Ag/γ-–Al₂O₃. When Ag/Al–Gd-x photocatalysts were tested, the 4-ClPh photoconversion was improved and more than 90.0% of 4-ClPh was photoconverted after 3 h of UV light irradiation in the materials containing 15.0 and 25.0 wt% of Gd₂O₃. Ag/Al–Gd-25 was the material with the highest efficacy to mineralize dissolved organic carbon, mineralizing more than 85.0% after 4 h of UV light irradiation. Silver nanoparticles and micro-particles of irregular pentagonal shape intersected by plane nanobelts of Al₂O₃–Gd₂O₃ composite oxide were detected in the Ag/Al–Gd-25 photocatalyst. This material is characterized by a lowest recombination rate of electron–hole pairs. The low recombination rate of photo-induced electron–hole pairs in the Ag/Al–Gd-x photocatalysts with high Gd₂O₃ contents (≥15.0 wt%) confirmes that the presence of silver nanoparticles and microparticles interacting with Al₂O₃–Gd₂O₃ composite oxide entities favors the separation of photo-induced charges (e⁻ and h⁺). These materials could be appropriate to be used as highly efficient photocatalysts to eliminate high concentrations of 4-ClPh in aqueous medium.

Ag/Al₂O₃–Gd₂O₃ showed high efficacy to photodegradate 4-chlorophenol, the strong interaction between silver nano-particles and micro-particles and Al₂O₃–Gd₂O₃ entities favors the decrease in the recombination rate.     

Continuous selective deoxygenation of palm oil for renewable diesel production over Ni catalysts supported on Al2O3 and La2O3–Al2O3

The present study provides, for the first time in the literature, a comparative assessment of the catalytic performance of Ni catalysts supported on γ-Al₂O₃ and γ-Al₂O₃ modified with La₂O₃, in a continuous flow trickle bed reactor, for the selective deoxygenation of palm oil. The catalysts were prepared via the wet impregnation method and were characterized, after calcination and/or reduction, by N₂ adsorption/desorption, XRD, NH₃-TPD, CO₂-TPD, H₂-TPR, H₂-TPD, XPS and TEM, and after the time-on-stream tests, by TGA, TPO, Raman and TEM. Catalytic experiments were performed between 300–400 °C, at a constant pressure (30 bar) and different LHSV (1.2–3.6 h⁻¹). The results show that the incorporation of La₂O₃ in the Al₂O₃ support increased the Ni surface atomic concentration (XPS), affected the nature and abundance of surface basicity (CO₂-TPD), and despite leading to a drop in surface acidity (NH₃-TPD), the Ni/LaAl catalyst presented a larger population of medium-strength acid sites. These characteristics helped promote the SDO process and prevented extended cracking and the formation of coke. Thus, higher triglyceride conversions and n-C₁₅ to n-C₁₈ hydrocarbon yields were achieved with the Ni/LaAl at lower reaction temperatures. Moreover, the Ni/LaAl catalyst was considerably more stable during 20 h of time-on-stream. Examination of the spent catalysts revealed that both carbon deposition and degree of graphitization of the surface coke, as well as, the extent of sintering were lower on the Ni/LaAl catalyst, explaining its excellent performance during time-on-stream.

Highly selective and stable Ni supported on La₂O₃–Al₂O₃ catalyst on the deCO/deCO₂ reaction paths for the production of renewable diesel.     

Chemical looping steam reforming of glycerol for hydrogen production over NiO–Fe2O3/Al2O3 oxygen carriers

Fe-based oxygen carriers (OCs) are widely used in chemical looping steam reforming (CLSR) due to excellent resistance to carbon buildup, low toxicity, and high activity. In this study, a type of nano NiO–Fe₂O₃/Al₂O₃ Fe-based OC that can easily be reduced by fuels and re-oxidized by air was developed for use in glycerol CLSR. It was synthesized by co-precipitation and impregnation. Based on the quadratic regression orthogonal model, a quadratic polynomial function was established to investigate the effects of temperature (T), water/carbon ratio (S/C), and loading (M) on hydrogen content (HL) and hydrogen selectivity (S). The OCs were characterized by XRD, XPS, SEM/EDX-mapping, TEM, and H₂-TPR to determine their physicochemical properties. XPS shows the Fe phase highly interacted with the Al₂O₃ supporting matrix by forming Fe aluminates in NiO–Fe₂O₃/Al₂O₃. The S (85.33%) and HL (78.41%) were obtained under the optimal conditions T = 600 °C, S/C = 1.0 mol mol⁻¹ and M = 0. A hydrogen content fluctuation within 4% was obtained under T = 700 °C, S/C = 1.0 mol mol⁻¹, and M = 2.5%, which means the cycle stability is perfect because of the addition of Ni. This study provides a basis for the development of efficient oxygen carriers in the CLSR system.

A nano NiO–Fe₂O₃/Al₂O₃ Fe-based OC was developed for CLSR hydrogen production experiments in a modified device. Ni promoted Fe-Al2O3 is effective and stable.