NH3 Temperature-programmed Desorption Research Articles

Ga-doped spinel-typed Co-Al catalysts for CO2-assisted ethane dehydrogenation

A series of Ga-doped spinel-typed Co-Al catalysts were prepared via one-step evaporation-induced self-assembly (EISA) method. These catalysts present promising catalytic performance for CO2-assisted ethane dehydrogenation, which can be ascribed to the conjunction effect of cobalt and gallium species. The incorporation of Ga into the structure of Co-Al spinel has been recognized for enhancing CO2 conversion via reverse water-gas shift reaction, leading to a favorable equilibrium shift towards ethylene, along with an improved catalyst stability as a result of coexisting Boudouard reaction. Through X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), NH3 and CO2 temperature-programmed desorption (TPD) characterizations, coordinatively unsaturated Co2+ and Ga3+ cations were identified as collaborative catalytic active sites, with gallium species taking the prominent role. These sites were closely associated with the formation of acid-base pairs on the catalyst surface, which were crucial for the adsorption and activation of the reactants.

Catalytic hydrogenation of CO2 to aromatics over indium-zirconium solid solution and sheet HZSM-5 tandem catalysts

The presence of acids and bases, coupled with its exceptional CO2 adsorption capacity and thermal stability, has established zirconia as a highly esteemed promoter and carrier. Researchers have found that the In2O3 supported ZrO2 exhibits high activity and remarkable stability. Therefore, xIn-yZr(T) solid solutions were prepared with different calcination temperatures and In/Zr molar ratios. The solid solutions were then combined with sheet HZSM-5 zeolite from tandem catalysts, which were investigated for their catalytic performance in converting CO2 to aromatics. The X-ray diffraction, scanning electron microscopy, N2 adsorption-desorption, NH3 temperature-programmed desorption, pyridine infrared radiation, X-ray photoelectron spectroscopy, electron paramagnetic resonance, CO2 temperature-programmed desorption and H2 temperature-programmed reduction characterization methods were used to investigate the physicochemical properties of catalysts. Density Functional Theory calculations were used to investigate the energy of thermal desorption and H2 reduction to generate oxygen vacancies on the surface of In2O3(111) and Zr/In2O3(111). Additionally, the influence of oxygen vacancies on CO2 adsorption energies was simulated. It was found that the incorporation of a moderate amount of zirconium carriers promoted the generation of oxygen vacancies and provided better metal-carrier interactions. The 4In-1Zr(500 °C)/HZSM-5 tandem catalyst exhibits excellent catalytic stability, achieving a CO2 conversion of 24.3 % and aromatics selectivity of 37.3 %.

Zeolite-templated carbon synthesized with ion-exchanged FAU-zeolite using alkaline earth metal ions for the selective adsorption of C2 hydrocarbons over C1 hydrocarbon

In this study, zeolite-templated carbon (ZTC) was synthesized using ion-exchanged faujasite-Y (FAU, NaY) zeolites with different alkali earth metals (Mg2+, Ca2+, Sr2+, and Ba2+) to investigate the effects of these metals on the synthesis, characteristics, and C2/C1 hydrocarbon separation performance of ZTC. Thermogravimetric and temperature-programmed desorption of NH3 (TPD-NH3) analyses showed that carbon deposition tends to occur outside the pores because of the increasing number of moderate acid sites as the atomic number increases. In particular, in the case of FAU-ZTC(Ca) synthesized using CaY as the ZTC template, carbon accumulated inside the pores owing to the distribution of the appropriate acid strength, resulting in the highest specific surface area of 2,835 m2/g among the synthesized ZTCs. The combined X-ray photoelectron and Raman spectroscopy results confirm that these defect sites of ZTC act as adsorption sites for large molecules such as C2H4 and C2H6. The isothermal adsorption of CH4, C2H4, and C2H6 showed that FAU-ZTC(Ca) exhibited the highest adsorption capacity ratios of C2H4 and C2H6 to CH4, with a C2H6/CH4 ratio of 5.897 and C2H4/CH4 ratio of 5.288, respectively. The effective pore size ranges affecting the adsorption of CH4, C2H4, and C2H6 determined using linear regression analysis are 0.4 to 0.6 nm for CH4 and 0.6 to 1.1 nm for C2H4 and C2H6. Molecular simulations confirmed that the adsorption energy was maximized by the interaction between the hydrogen atoms of the hydrocarbons and the carbon atoms of ZTC. Furthermore, C2H4 and C2H6 require larger pores than CH4 adsorption because C2H4 and C2H6 prefer to lie horizontally rather than vertically in the pores of the ZTC.

Insights into the Acidic Site in Manganese Oxide in Terms of the Sulfur and Water Tolerance of Low-Temperature NH3 Selective Catalytic Reduction.

A critical constraint impeding the utilization of Mn-based oxide catalysts in NH3 selective catalytic reduction (NH3-SCR) is their inadequate resistance to water and sulfur. This vulnerability primarily arises from the propensity of SO2 to bind to the acidic site in manganese oxide, resulting in the formation of metal sulfate and leading to the irreversible deactivation of the catalyst. Therefore, gaining a comprehensive understanding of the detrimental impact of SO2 on the acidic sites and elucidating the underlying mechanism of this toxicity are of paramount importance for the effective application of Mn-based catalysts in NH3-SCR. Herein, we strategically modulate the acidity of the manganese oxide catalyst surface through the incorporation of Ce and Nb. Comprehensive analyses, including thermogravimetry, NH3 temperature-programmed desorption, in situ diffused reflectance infrared Fourier transform spectroscopy, and density functional theory calculations, reveal that SO2 exhibits a propensity for adsorption at strongly acidic sites. This mechanistic understanding underscores the pivotal role of surface acidity in governing the sulfur resistance of manganese oxide.

Low Content Ga2O3 Enables the Direct Methane Conversion.

The direct conversion of methane (CH4), a main greenhouse gas, to value-added chemicals has attracted increasing attention in order to alleviate the current energy crisis and environmental concern. Nevertheless, the oriented conversion of CH4 to target product is formidably challenging due to the inertness of CH4. In this work, we demonstrate that zeolite modified by a low amount of Ga2O3 (GS-1) can serve as a highly active and stable catalyst for direct conversion to hydrogen (H2) and solid carbon. The optimal GS-1 with 0.62 wt % of Ga displays a CH4 conversion rate of 70.6 mol/gGa/h with a H2 productivity of 134 mol/gGa/h at 800 °C. Analysis on NH3 temperature-programmed desorption (TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) suggests that the introduction of Ga2O3 can poison the acidic site of zeolite and promote the dehydrogenation of CH4. This work reports a highly active and stable catalyst for direct methane conversion, which may provide a feasible strategy for the sustainable utilization of CH4.

Unraveling the Structure-Activity-Stability Relationship over Gallium-Promoted HZSM-5 Nanocrystalline Aggregates for Propane Aromatization.

The aromatization of light alkane is an important process for increasing the aromatic production and utilization efficiency of light alkane resources simultaneously. Herein, Ga-modified HZSM-5 catalysts were prepared and investigated by a series of characterization techniques such as X-ray diffraction, nuclear magnetic resonance spectroscopy, transmission electron microscopy, N2 adsorption-desorption, and NH3 temperature-programmed desorption to study their physicochemical properties. The catalytic performance in propane aromatization was also tested. Importantly, the structure-activity relationship, reaction pathway, and coke formation mechanism in propane aromatization were systematically explored. It was found that different Ga introduction methods would affect the amounts of Brønsted and Lewis acid sites, and Ga-HZSM-5 prepared by the hydrothermal method exhibited higher amounts of Brønsted and Lewis acid sites but a lower B/L ratio. As a result, Ga-HZSM-5 showed higher propane conversion and benzene, toluene, and xylene yield compared with that of Ga2O3/HZSM-5. The propane aromatization reaction pathway indicated that propane dehydrogenation to propene was a crucial step for aromatic formation. The increase of the Lewis acid density in Ga-HZSM-5 can effectively improve the dehydrogenation rate and promote the aromatization reaction. Furthermore, the formation of coke species was studied by thermogravimetry-mass spectrometry and Raman approaches, the results of which indicated that the graphitization degree of coke formed over spent Ga-HZSM-5 is lower, resulting in enhanced anticoking stability.

Highly Efficient PtSn/Al2O3 and PtSnZnCa/Al2O3 Catalysts for Ethane Dehydrogenation: Influence of Catalyst Pretreatment Atmosphere

Increased demand for ethylene has motivated direct ethane dehydrogenation over Pt-based catalysts. PtSn/γ-Al2O3 and PtSnZnCa/γ-Al2O3 catalysts were investigated with the aim of understanding the effect of the pretreatment environment on the state of dispersed Pt for ethane dehydrogenation. The catalysts were prepared by the impregnation method and pretreated in different environments like static air (SA), flowing air (FA), and nitrogen (N2) atmospheres. A comprehensive characterization of the catalysts was performed using Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), Temperature-Programmed Reduction (TPR), NH3 Temperature-Programmed Desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), and Transmission Electron Microscopy (TEM) techniques. The results reveal that the PtSn on Al2O3 catalyst pretreated in the static air environment (PtSn-SA) exhibits 21% ethylene yield with 95% selectivity at 625 °C. XPS analysis found more platinum and tin on the catalyst surface after static air treatment. The overall acidity of the catalysts decreased after thermal treatment in static air. Elemental mapping demonstrated that Pt agglomeration was pronounced in catalysts calcined under flowing air and nitrogen. These factors are responsible for the enhanced activity of the PtSn-SA catalyst compared to the other catalysts. The addition of Zn and Ca to the PtSn catalysts increases the yield of the catalyst calcined in static air (PtSnZnCa-SA). The PtSnZnCa-SA catalyst showed the highest ethylene yield of 27% with 99% selectivity and highly stable activity at 625 °C for 10 h.

Engineering binary CrmNb1-mOx (m = 0.1, 0.3, 0.5) oxides catalysts to enhance its NH3-SCR denitration activity and SO2 resistance: Study on the influence of redox property and acidity

It is still a challenge to create novel simply environmentally friendly NH3-SCR denitration catalysts in presence of SO2 and H2O, and to further understand the role of redox property and acidity of catalyst. In this work, a series of binary CrmNb1-mOx (m = 0.1, 0.3 and 0.5) oxides with different Cr/Nb ratio were engineered for NH3-SCR denitration by using the citric acid complex method. Among these catalysts, Cr0.3Nb0.7Ox revealed best catalytic performance with over 90 % NO conversion in the range of 210–390 ℃ and great SO2 and H2O resistance. The effects of different Cr/Nb ratio on catalytic activity was investigated though following characterization such as Raman spectroscopy, Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), N2 physical adsorption, NO-Temperature programmed desorption (NO-TPD), H2-Temperature program reduction (H2-TPR), X-ray photoelectron spectra (XPS), NH3-Temperature programmed desorption (NH3-TPD) and In situ Diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTS). The impact of surface redox property and acidity on catalytic performance was further investigated by changing the Cr/Nb ratio. The results suggest that different Cr/Nb ratio result in catalysts having different Brunauer-Emmett-Teller (BET) surface area, and variation of crystal structure, generating the improvement of the surface acid amount and the enhancement of the oxidizing ability due to existence of more surface active oxygen species. Besides, the results of in situ DRIFTS verify that more acid sites are exposed on the Cr0.3Nb0.7Ox surface and react with absorbed NOx even in the existence of SO2, which followed Langmuir-Hinshelwood (L-H) mechanism.

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.

Polymorphism and Its Influence on Catalytic Activities of Lanthanide-Glutamate-Oxalate Coordination Polymers.

To study the relationship between polymorphism and catalytic activities of lanthanide coordination polymers in the cycloaddition reactions of CO2 with epoxides, the monoclinic and triclinic polymorphs of [LnIII(NH3-Glu)(ox)]·2H2O, where LnIII = LaIII (I), PrIII (II), NdIII (III), SmIII (IV), EuIII (V), GdIII (VI), TbIII (VII), and DyIII (VIII), NH3-Glu- = NH3+ containing glutamate, and ox2- = oxalate, were synthesized and characterized. Factors determining polymorphic preference, the discrepancy between the two polymorphic framework structures, potential acidic and basic sites, thermal and chemical stabilities, active surface areas, void volumes, CO2 sorption/desorption isotherms, and temperature-programmed desorption of NH3 and CO2 are comparatively presented. Based on the cycloaddition of CO2 with epichlorohydrin in the presence of tetrabutylammonium bromide under solvent-free conditions and ambient pressure, catalytic activities of the two polymorphs were evaluated, and the relationship between polymorphism and catalytic performances has been established. Better performances of the monoclinic catalysts have been revealed and rationalized. In addition, the scope of monosubstituted epoxides was experimented and the outstanding performance of the monoclinic catalyst in the cycloaddition reaction of CO2 with allyl glycidyl ether under ambient pressure has been disclosed.

Fabrication of 3-(trihydroxysilyl)-1-propanesulfonic acid membranes with superior affinity and selectivity for NH3 permeation over H2 and N2 at 50–300 °C

Ammonia (NH3) produced by Haber-Bosch process is separated through the condensation process, which needs a large amount of energy consumption. Membrane separation technology is compelling for achieving energy-saving and efficient NH3 separation. Therefore, 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS) was applied, for the first time, to fabricate sulfonic silica-based membranes and evaluated for NH3 selective permeation. The amorphous siloxane network can be formed by simple condensation of silanol (Si–OH) under sulfonic acid (-SO3H) self-catalysis, as confirmed by the results of Fourier transform infrared spectroscopy and X-Ray diffractometry. Moreover, TPS xerogel powders dried from TPS sols showed excellent thermal stability and dense structure via thermogravimetric and N2 adsorption analyses. Importantly, an intensive NH3 adsorption amount of ∼3.0 mmol g−1 for TPS xerogels from NH3 adsorption and temperature-programmed desorption was twice higher than the reported oxidized (3-mercaptopropyl)trimethoxysilane xerogels (∼1.41 mmol g−1), which was ascribed to the inherently stronger proton-acidic -SO3H groups in TPS. Finally, TPS membranes prepared using TPS solutions diluted with ethanol expressed superior NH3-selective permeation based on favorable molecular sieving and NH3 adsorption-diffusion via single and binary gas permeation, especially remarkable NH3 permeance of ∼2.6 × 10−7 mol m−2 s−1 Pa−1 and excellent NH3/N2 selectivity of 266 at 300 °C.

In situ Ni2P catalyst for the selective processing of terephthalic acid into BTX fraction

In situ obtained Ni2P-based catalysts were proposed for the selective conversion of terephthalic acid into the benzene-toluene-xylene fraction. The catalysts were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and NH3 temperature-programmed desorption. The influence of reaction time, temperature and H2 pressure on the conversion of terephthalic acid and benzene-toluene-xylene selectivity was studied. Direct deoxygenation and decarboxylation were found to be the main reaction pathways using in situ Ni2P catalysts. Selectivity for the benzene-toluene-xylene fraction reached up to 100 % (at full terephthalic acid conversion) under moderate reaction conditions. The reusability of the in situ Ni2P catalyst before and after regeneration was demonstrated.

Valorisation of microalga Chlorella sp. into furans in the presence of Nb2O5 catalysts

Despite the interest in niobia-based catalysts and the importance of biomass valorisation, studies on these catalysts typically utilize model substrates like simple sugars. In this study, a series of niobium oxide-based catalysts was prepared for the application in aqueous phase catalytic conversion of sugars extracted from Chlorella sp. microalga into value-added furans. The solid catalysts were firstly characterized by various techniques including X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Raman and X-ray photoelectron (XPS) spectroscopy as well as low-temperature N2 physisorption. Moreover, the acidity of the catalysts was assessed by using the temperature-programmed NH3 desorption (NH3-TPD), by titration of water suspended catalyst with NaOH solution, and by P-bearing molecular probes loaded catalysts through 31P and 1H solid-state nuclear magnetic resonance (NMR) techniques. Herein, we focused on the catalytic transformation of Chlorella sp. and glucose solution as model molecule into furans. The best Nb2O5 catalysts for valorizing Chlorella sp. into furans exhibited a larger number of Brønsted acid sites, achieving conversion yields to 5-HMF and furfural of ca. 20–22 % with respect to the extracted sugars from algae. The results showed a discernible dependence of the conversion yields to 5-HMF and furfural on catalyst acidity, specific surface area, and the presence of the Brønsted acid sites. Conversely, when using the glucose solution as substrate is concerning, the highest yield to 5-HMF was reached by using a catalyst that showed also the presence of Lewis acid sites. A systematic investigation of the structure–activity relationships in niobium oxide application for aqueous phase dehydration using real biomass substrates to obtain furanic derivatives has not been documented thus far. Therefore, the current research is significant as it demonstrates the feasibility of transforming the carbohydrate content in microalgal biomass into furans by identifying the best catalyst to use.

Nickel-containing catalysts for ethylene conversion to motor fuel components and light alkenes

Polyfunctional Ni-containing catalysts supported on the B2O3-Al2O3 and MoO3-Al2O3 were prepared by a sequential impregnation. They were evaluated in ethylene conversion to C5+ alkenes or propylene. The catalysts were characterized by X-ray diffraction, Fourier transformed infrared spectroscopy, Fourier transformed infrared spectroscopy of adsorbed CO, UV-VIS diffuse reflectance spectroscopy, temperature programmed reduction and temperature-programmed desorption of NH3. NiO/B2O3-Al2O3 samples containing Ni2+ cations chemically bonded to the acid support are the most effective catalysts for ethylene oligomerization. The NiO/MoO3-Al2O3 catalyst activity in the ethylene conversion to propylene is related with the presence of ethylene dimerization active sites, i.e. Ni2+ cations bonded to the support acidic sites, and active sites of metathesis in the form of monomolybdate species.

Impact of microporous zeolite-coated macroporous supports on the catalytic pyrolysis of methylcyclohexane under supercritical conditions

Under supercritical conditions, the effects of the microporous zeolite-coated macroporous supports (i.e., ceramic-supported ZSM-5 catalysts and metal-supported ZSM-5 catalysts) on the endothermic pyrolysis process of methylcyclohexane (MCH, CH3C6H11) were examined. The micro-macroporous composite materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and NH3 temperature-programmed desorption (NH3-TPD) analysis. ZSM-5-coated Al2O3 hollow fiber and ZSM-5-coated NiCrFeAl metal foam were both tested using an isothermal constant-pressure continuous-flow heterogeneous catalytic reactor at high temperature (550 °C) and pressure (50 bar) that simulate supersonic jet engines. The MCH pyrolysis conversions and post-pyrolysis products were determined by gas chromatography, while the deposited coke on the microporous zeolite catalysts was quantified using thermogravimetric (TG) analysis. ZSM-5-coated NiCrFeAl metal foam catalyst showed a slightly higher MCH pyrolysis conversion (%) than ZSM-5-coated Al2O3 hollow fiber catalyst. On the other hand, the ZSM-5-coated Al2O3 hollow fiber produces fewer aromatic hydrocarbons (benzene, toluene, and xylene, BTX), as well as cyclic or polycyclic hydrocarbons (naphthalene). Additionally, the coke deposition was approximately 2 times lower on the ZSM-5-coated Al2O3 hollow fiber catalyst compared to the ZSM-5-coated NiCrFeAl metal foam. Furthermore, due to the endothermic nature of the catalytic pyrolysis of MCH under supercritical jet conditions over the studied microporous zeolite-coated macroporous supports, a temperature decrease of approximately 15–20 °C was observed.

Catalytic Hydrogenation Property of Methyl Benzoate to Benzyl Aldehyde over Manganese-Based Catalysts with Appropriate Oxygen Vacancies

The synthesis of benzaldehyde, a compound widely utilized in food, medicine, and cosmetics, was achieved through a one-step catalytic hydrogenation using the cost-effective raw material, methyl benzoate. This process aligns with the principles of atom economy and green production. Despite the development of numerous high-performance catalysts by scholars, the challenge remains in achieving lower reaction temperatures, ideally below 400 °C. In this study, a series of MnOx/γ-Al2O3 catalysts were meticulously prepared using the precipitation-impregnation method. These catalysts featured supports calcined at various temperatures and distinct manganese active components. Characterization techniques such as X-ray diffraction (XRD), N2 physical adsorption, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), H2 temperature programmed reduction (H2-TPR), and NH3 temperature-programmed desorption (NH3-TPD) were employed to analyze the structure and surface properties of the catalysts. Notably, the optimized reaction temperature was found to be 360 °C. The catalyst exhibited the most favorable performance when the calcination temperature of the support was 500 °C and the Mn/Al molar ratio reached 0.18. Under these conditions, the catalyst demonstrated the most suitable oxygen vacancy concentration, yielding impressive results: a conversion rate of 87.90% and a benzaldehyde selectivity of 86.1%. These achievements were attained at 360 °C, atmospheric pressure, a hydrogen to methyl benzoate molar ratio of 40:1, and a Gas Hourly Space Velocity (GHSV) of 800 h−1. This research underscores the potential for optimizing catalysts to enhance the efficiency and sustainability of benzaldehyde synthesis.

Oxidative carbonylation of methane into acetic acid: Effect of metal (Zn, Cu, La, and Mg) doping on Rh/ZSM-5 activity

It was shown that the nature and method of the second element-modifier (Zn, Si, La, and Mg) introduction have a significant effect on the acidic properties of the zeolite catalysts and the active component (Rh) localization, which leads to a change in their catalytic properties in the oxidative methane carbonylation into acetic acid. The most active second components were Cu and Zn, introduced by impregnation (acetic acid yield was 919 and 819 μmol·gcat−1, respectively). Using temperature-programmed desorption of NH3, Fourier-transform infrared spectroscopy of pyridine adsorption and X-ray photoelectron spectroscopy it was found that an improvement of catalyst efficiency was associated with an increased acidity and a greater content of Brѳnsted acid sites together with an increase in the proportion of Rh atoms inside microporous channels and/or channel intersection voids, that are active in the acetic acid formation.

Effects of transition metal doping on the properties and catalytic performance of ZSM-5 zeolite catalyst on ethanol-to-hydrocarbons conversion

In this study, the effects of transition metal-doping on the physicochemical properties and catalytic performance of HZSM-5 catalysts for the conversion of ethanol to hydrocarbons are investigated using experimental data and secondary data from the literature. Hydrothermally synthesized novel ZSM-5 catalysts were modified with different concentrations (0.5 and 10 wt%) of transition metals (Co, Fe, Ni). Characterizations, including X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, particle size distribution, N2 adsorption and NH3 temperature-programmed desorption, revealed the changes in catalyst properties. The introduction of transition metals affected the surface area, particle size and acidity without altering the MFI structures. In particular, a reduction in surface area was observed, ranging from 2.6 to 23 %, corresponding to the different metal loading of 0.5–10 wt% compared to the surface area of the pure catalyst (397.5 m²/g). In addition, metal-doping led to an increase in Lewis acid sites, accompanied by a decrease in strong acid sites. Catalytic evaluation at 350 °C and a space velocity of 12 h−1 showed improved performance in metal-doped ZSM-5 catalysts, which exhibited high selectivity towards fuel-range hydrocarbons, compared to the unmodified catalyst. Catalysts with low metal doping showed optimal catalytic activity, while high metal doping led to increased coke deposition and deactivation of the catalyst due to an increased concentration of strong acids. These results underline the suitability of metal-modified ZSM-5 for hydrocarbon reactions and provide valuable insights for the optimization of catalysts for ethanol conversion to fuel-range hydrocarbons.

Ce doped V-W/Ti as selective catalytic reduction catalysts for cement kiln flue gas denitration.

In cement industry, the selection of catalyst temperature window and the inhibition effect of dust composition in flue gas on catalyst are the key issues of flue gas denitrification. In this article, a pilot study with Ce doped V-W/Ti catalyst on the removal of NOx by selective catalytic reduction with ammonia (NH3-SCR) from the cement kiln flue gas was presented. Cement kiln dust loading on catalysts obviously decreased the NO conversion in the absence of SO2 and H2O, while the denitration efficiency restored from 75 to 98% at 280 ℃ after SO2 and H2O introduced into the reaction system, which mainly because the SO2 may enhance the acidic site on the catalyst surface, and prefer to be bonded with the coordinated Ca species, releasing the active sites poisoned by dust. The NH3-temperature programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR) detections were performed to reveal that the appropriate Ce and W ratios catalyst contributed better denitrification activity. The optimum ratio of Ce doped catalyst was amplified to form the standard honeycomb monomer catalyst, and then, the activity of catalyst was verified on the side line of cement kiln. The effect of temperature and space velocity on denitrification efficiency was investigated, and the denitration efficiency reached to 92.5% at 300℃ and 3000h-1 space velocity. Moreover, the life of catalyst was verified and predicted by GM (1,1) grey model. The study realized the innovation from the laboratory data rules to the industrial pilot application, providing positive promoting value for the industrial large-scale demonstration application of the catalyst.

Carbon dioxide hydrogenation combined with an oxidative methane carbonylation over CeO2-HZSM-5 catalyst for acetic acid production

Utilization of CO2 into high value-added products, in particular acetic acid, is a promising and in turn challenging strategy. This issue could be resolved using bifunctional CeO2-HZSM-5 catalyst, which simultaneously promotes the CO2 hydrogenation and oxidative methane carbonylation in a one-pot synthesis. Bulk CeO2, HZSM-5 zeolite, and their mechanical mixture were compared in the tandem transformations of CO2, CH4, and CO into acetic acid. The catalysts were analyzed using N2 adsorption-desorption, NH3-TPD, CO2-TPD, XRD, XRF, and Raman spectroscopy. It was shown that CeO2-HZSM-5 yields 0.74 μmol·g−1·h−1 of acetic acid, whereas CeO2 and HZSM-5 give 0.46 and 0.37 μmol·g−1·h−1, respectively. At the same time, the selectivity to acetic acid on CeO2-HZSM-5 is 54.0, as opposed to 26.4 % and 8.6 % on CeO2 and HZSM-5, respectively. Thus, according to the catalytic studies along with the temperature-programmed desorption of NH3 and CO2, metal oxide and zeolite components of CeO2-HZSM-5 physical mixture were established to exhibit the improved performance in the acetic acid production caused by the combined effect of CeO2 base sites and HZSM-5 acid sites. In addition, CeO2-HZSM-5 demonstrates an excellent catalyst stability during 100 h reaction exposure at 500 °C without pronounced reduction of activity and selectivity.