Infrared Spectroscopy Of Pyridine Adsorption Research Articles

Evaluating CO2 desorption performance of MEA solution with MnOx/HZ catalytic packings by visualization method

The high energy consumption in the CO2 desorption process is one of the main issues of the chemical absorption method. To address this issue, a MnOx modified HZSM-5 catalyst (MnOx/HZ) was prepared by impregnation method and used as catalytic packing to improve the CO2 desorption rate in the monoethanolamine (MEA) solution. Since the catalytic effects mainly work around the catalytic packing, a visualization method, which can measure the CO2 desorption rate per unit surface area (vCO2/area) of a single packing, is proposed to avoid some uncertain effects occurring as the conventional bubbling method is used. The results showed that the vCO2/area of the MnOx/HZ catalytic packing is 10.06 μmol·cm−2·s−1 at 80 °C, which is 1.78 times of that of HZSM-5 and 15 to 60 times of that of commercial packings. Actually, the MnOx/HZ has more Brønsted and Lewis acid sites than HZSM-5 according to the pyridine adsorption infrared spectroscopy (Py-IR) characterization. As a result, the apparent activation energy (Ea) of the CO2 desorption reaction with the addition of MnOx/HZ can be reduced by 58.6% and 18% compared with the addition of ceramic saddle ring packing and HZSM-5, respectively. However, the catalytic performance of MnOx/HZ packings degrades gradually due to the blockage of micropores by the reaction product, that needs to be settled in the future.

CoZn@N-ALC, highly-efficient magnetic Co nanoparticles anchored by lignin-based Nitrogen-doping carbon for hydrodeoxygenation of vanillin

The conversion of lignin-based platform compounds into valuable biofuels and chemicals through catalytic processes is an attractive approach for the efficient valorization of renewable lignocellulosic biomass. One such process is the hydrodeoxygenation (HDO) of lignin-based vanillin (VL) to produce 2-methoxy-4-methylphenol (MMP), which is a promising liquid fuel and intermediate for fine chemicals. However, the development of a cost-effective catalytic system with high activity and selectivity remains a challenge. In this study, we report the preparation of a highly-efficient magnetic Co nanoparticles catalyst, CoZn@N-ALC, using alkali lignin as an assembly macromolecular ligand, Zn as a sacrificial metal, and dicyandiamide as a nitrogen source before the pyrolysis process. Various characterization techniques, including powder X-ray diffraction (XRD), pyridine adsorption infrared spectroscopy (Py-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), isothermal nitrogen adsorption/desorption, and X-ray photoelectron spectroscopy (XPS), were employed to investigate the role of zinc and nitrogen in the construction process of CoZn@N-ALC and the influence of catalyst preparation conditions. The optimized CoZn@N-ALC catalyst demonstrated nearly 100 % conversion of VL, complete selectivity towards MMP, and easy separation from the aqueous HDO system. Structure-performance investigation and density functional theory (DFT) calculations suggest that the exceptional catalytic performance of this catalyst can be attributed to the selective adsorption of C=O bonds by abundant Co (111) active species and its Lewis acid sites. This work provides valuable insights into the rational design of efficient, non-noble metal nanoparticle catalysts based on alkali lignin for the conversion of lignin-based platform compounds.

Enhanced CO2 desorption rate for rich amine solution regeneration over hierarchical HZSM-5 catalyst

High energy consumption during the carbon dioxide (CO2) desorption process in amine-based CO2 capture technology is a crucial hindrance to achieving carbon neutrality. HZSM-5 is one of the most widely reported solid acid catalysts used in primary amine regeneration. This work compared a series of HZSM-5 zeolites with different Si/Al ratios in terms of CO2 desorption performance. To further enhance catalytic activity, hierarchical HZSM-5 was synthesized by the dealumination and desilication re-assembly method with different acid and alkali concentrations. The experimental results suggested that desilication by modification in sodium hydroxide resulted in a significant improvement of mesoporous surface area. The NaOH-0.4 catalyst could improve the amount of desorbed CO2 by 40.3% and decrease the relative heat duty by 28.5%. And the cyclic tests revealed that catalytic activity was well preserved in the recycling process. Moreover, the structure and acidity of modification samples were characterized by X-Ray diffraction (XRD), Fourier transforms infrared (FT-IR), Nitrogen adsorption–desorption experiment, temperature programmed desorption of ammonia (NH3-TPD), Pyridine-adsorption infrared spectroscopy (Py-IR), and scanning electron microscopy (SEM). The characterization results suggested that the synergistic effect of larger mesoporous surface area and total acid sites was important to enhance catalytic CO2 desorption performance. These results showed a new understanding of catalyst design for CO2 capture technology by modifying the structure of the catalyst support.

Metal-organic frameworks-derived manganese trioxide with uniformly loaded ultrasmall platinum nanoparticles boosting benzene combustion

Four morphologies of metal-organic frameworks derived Mn2O3 were prepared by calcination of metal-organic frameworks self-assembled from metal ions and organic ligands and loaded with platinum. The catalyst showed excellent catalytic performance for benzene (T90% = 131 °C). ESR (electron spin resonance) test showed that due to the strong electron metal support interaction between Pt and Mn2O3, there were a large number of oxygen vacancies on the surface of the catalyst as active sites to promote the oxidation of benzene. The presence of a large number of Lewis acid sites on the catalyst surface was confirmed by Py-IP (Pyridine adsorption infrared spectroscopy) test. The intermediates of benzene catalytic oxidation are ethyl acetate, carboxylic acids and aldehydes, which can be verified by in-situ DRIFTS. In summary, the catalysts synthesized in this work provide a novel perspective for combining metal-organic frameworks-derived oxides and precious metals for the catalytic oxidation of volatile organic compounds.

Preparation and application of ZrO2–SiO2 complex oxide for efficient biocrude generation by hydrothermal liquefaction of Spirulina

Catalysts act a pivotal part in hydrothermal liquefaction (HTL), which is a efficient technology for converting biomass into bioenergy. Herein, atom-doped ZrO2–SiO2 complex oxide catalysts were prepared for HTL of Spirulina to produce biocrude. In this study, sol–gel method was adopted to prepare the catalysts. Calcination temperature, surfactant type and dosage, ratio of SiO2 to ZrO2 were analyzed for optimizing biocrude yield. Physicochemical properties of ZrO2–SiO2 catalysts were conducted by X-ray diffraction, thermogravimetric analysis, N2 adsorption–desorption and infra-red spectroscopy of pyridine adsorption. The result showed that the catalysts that calcinated at 700°C with the ratio of SiO2:ZrO2 = 10:1, 5g polyethylene glycol applied in the sol precursor achieved the best performance: specific surface area reached 461.86m2g−1 and the density of total acid site was up to 53.98mmolg−1, thereby it provided the highest biocrude yield as 55.8%, which contained the largest hydrocarbon content. Accordingly, ZrO2–SiO2 demonstrated promising catalyst ability in the field of HTL and could inspire related researchers screening HTL catalysts from certain aspects.

Catalytic fast pyrolysis of Arundo donax in a two-stage fixed bed reactor over metal-modified HZSM-5 catalysts

Various types of mono- and bi-metallic modified HZSM-5 catalysts such as Mo-, Fe-, Zn-, Cu-, Mo–Fe-, Mo–Zn-, and Mo–Cu-modified HZSM-5 were prepared via impregnation and were characterized by scanning electron microscope (SEM), inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and pyridine adsorption infrared spectroscopy (Py-IR) analysis. Online catalytic upgrading of Arundo donax pyrolysis vapors was performed using modified zeolite catalysts in a two-stage fixed bed reactor to investigate the catalytic performance. Results showed that loading of Mo, Fe, Zn and Cu were well-dispersed, the channels and acidity of zeolites were modified. Impregnation of HZSM-5 with metals resulted in relatively lower yield of oxygenates and nitrogen-containing compounds in bio-oil as compared to the reference condition without catalyst. Moreover, the addition of metals significantly favored the catalytic selectivity towards aromatics especially monocyclic aromatic hydrocarbons (MAHs). Mo-M/HZSM-5 catalysts was the best catalyst and exhibited the optimal de-oxygenation potential (from 62.66% to 18.03%), denitrification (from 6.53% to 0.43%) and produced maximum MAHs content approximately 28.77%. Among the bimetallic modified zeolite catalysts, Mo–Zn/HZSM-5 exhibited strong catalytic effect in oxygen-free aromatization of the mixed pyrolysis vapors containing methane and propane. In the presence of Mo–Zn/HZSM-5 catalyst, the content of oxygen in bio-oil decreased from 36.07 wt% to 15.05 wt%, and the calorific value reached a maximum value of 34.12 MJ kg−1. Mo–Zn/HZSM-5 has been identified as a superior catalyst for improving the value of Arundo donax pyrolysis to make bio-oil.

Synthesis of ethyl levulinate from cellulose over a double acid site catalyst

AbstractBACKGROUNDA novel double acid site solid catalyst (Al‐OCS‐0.1) having an ordered mesoporous structure was synthesized by grafting sulfonic acid groups on an oxidized ordered mesoporous carbon (OOMC) support and loading 10% Al2(SO4)3.RESULTAssessments using Field emission scanning electron microscopy, Transmission electron microscopy and X‐ray diffraction showed that the OMC structure remained unchanged after the chemical modification and Al2(SO4)3 loading. The Brunauer–Emmett–Teller surface area and average pore size of Al‐OCS‐0.1 decreased to 181 m2 g−1 and 7.1 nm after loading Al2(SO4)3, respectively. Ammonia temperature‐programmed desorption (NH3‐TPD) and Pyridine adsorption infrared spectroscopy (Py‐IR) demonstrated that Al‐OCS‐0.1 had abundant Brønsted and Lewis acid sites. The ammonia desorption of Al‐OCS‐0.1 increased from 2.0 to 7.2 mmol g−1 after loading Al2(SO4)3.CONCLUSIONThe Al‐OCS‐0.1 was used to catalyze the synthesis of ethyl levulinate from cellulose in ethanol and gave an extremely high yield of 50.8 mol% after 5 h at 200 °C. © 2021 Society of Chemical Industry (SCI).

Enhanced catalytic activity of Pt/H-ZSM-12 via alkaline post-treatment for the hydroisomerization of n-hexane

Abstract Bifunctional Pt/H-ZSM-12 catalysts with enhanced inter-mesoporosity were prepared from synthesized ZSM-12 samples by alkaline post-treatments with or without the presence of the template in the zeolite pores, ammonium ion-exchange, and impregnation with Pt(NH3)4Cl2. Different techniques, such as N2 adsorption-desorption, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), NH3 temperature-programmed desorption (NH3-TPD), and pyridine-adsorption infra-red spectroscopy (Py-IR), were used to characterize the synthesized samples. The prepared Pt/H-ZSM-12 catalysts were evaluated in the hydroisomerization of n-hexane. The results show that the template-containing ZSM-12 is a better parent for introducing abundant inter-mesopores by the alkaline post-treatment, accompanying with a better preservation of microporosity and strong acid sites, in comparison to the template-free ZSM-12 as the parent. In addition, the dispersion of Pt on the alkaline-treated zeolite is increased as well, which is also helpful to enhance the conversion of n-hexane and the selectivity for the dibranched hexanes.

Catalytic performance and mechanism of SO42−/ZrO2/SBA-15 catalyst for CO2 desorption in CO2-loaded monoethanolamine solution

The intensive energy requirement for rich solvent regeneration is the biggest obstacle to the widespread industrial application of amine-based CO2 capture technology. To address this challenge, here, for the first time, the composite catalysts SO42−/ZrO2/SBA-15 (SZS) with varying ZrO2 content were synthesized and then used to reduce heat duty for the CO2-loaded monoethanolamine (MEA) solution regeneration at 370.65 K. Additionally, the physicochemical properties of the prepared catalysts were characterized by various techniques, i.e. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption–desorption experiment, ammonia and CO2 temperature programmed desorption (NH3/CO2-TPD), and pyridine-adsorption infrared spectroscopy (Py-IR). The catalytic CO2 desorption performances of different catalysts (three SZS catalysts, SBA-15 and HZSM-5) were studied in terms of desorption rate, energy consumption and cyclic capacity. The experimental results show that the catalytic performance of SZS is better than the individual catalysts, and SZS can enhance the desorption factor by 100–200% and reduce the energy consumption by 20–26.50% compared to the blank run. Furthermore, the SZS catalysts have no negative influence on the CO2 absorption performance in terms of the absorption rate and have the advantages of good stability. Moreover, a possible catalytic mechanism in amine regeneration over SZS catalyst is proposed. This work may open a new avenue for rational generation of the novel catalysts for this priming catalyst-mediated CO2 desorption process and further advance the amine-based CO2 capture technology.

Reducing energy consumption of CO2 desorption in CO2-loaded aqueous amine solution using Al2O3/HZSM-5 bifunctional catalysts

The aim of this work is to find a potential way for great decrease in CO2 capture energy requirement. Here, for the first time, a series of bifunctional Al2O3/HZSM-5 catalysts (Al-ZSM) were prepared by the combined precipitation ultrasound method and used for the CO2 desorption process. All the investigated catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), N2 adsorption–desorption, ammonia and CO2 temperature programmed desorption (NH3/CO2-TPD) and pyridine-adsorption infrared spectroscopy (Py-IR). The regeneration behaviors of a 5 M monoethanolamine (MEA) solvent with four Al-ZSM catalysts were studied at an initial CO2 loading of 0.5 mol CO2/mol amine and the temperature of 96 °C. The results reveal that all the catalysts improve the CO2 desorption performance, the Al-ZSM catalysts show higher catalytic performance than the single catalysts Al2O3 and HZSM-5, and the Al-ZSM can reduce the heat duty by 23.3–34.2% as compared with the catalyst-free test. The use of Al-ZSM in the MEA regeneration process improves the desorption performance by 2–3 times in comparison with the blank run. A possible dual sites mechanism of CO2 desorption with Al-ZSM is suggested. The excellent performance of Al-ZSM can be attributed to their enhanced Brϕnsted acid sites (BAS), mesopore surface area (MSA) and basic sites, which resulted from the good synergistic reaction between the Al2O3 and HZSM-5, and the base treatment for HZSM-5. Besides, the stability test of the Al-ZSM was conducted. Based on the results, the Al-ZSM demonstrate a superior catalytic performance for the rich amine regeneration process, and present an excellent cyclic stability, explicitly have the potential to be a promising industrial catalyst for CO2 capture. Furthermore, the dual sites catalytic CO2 desorption over bifunctional catalysts will open a new path to design better catalysts for the rich amine solution regeneration process to increase the desorption performance, reduce the regeneration energy consumption, and thus further decreasing the operation costs of CO2 capture.

Catalytic performance of imidazole modified HZSM-5 for methanol to aromatics reaction

A facile approach was developed for the preparation of nano-sized HZSM-5 with a hierarchical mesoporous structure by adding imidazole into conventional zeolite synthesis precursor solution. The physicochemical properties of modified HZSM-5 were characterized by X-ray diffraction (XRD), N2 adsorption–desorption isotherms, scanning electron microscopy (SEM), NH3-temperature-programmed desorption (NH3-TPD) and pyridine adsorption infrared spectroscopy (Py-IR). The coke in spent catalysts was characterized by thermogravimetry (TG). The results showed that hierarchical HZSM-5 zeolites with excellent textural properties, such as abundant porous structure, uniform particle size and suitable acidity, could be synthesized by the recipe of one-pot synthesis routes. Moreover, the obtained HZSM-5 exhibited higher selectivity of total aromatics as well as longer lifetime in the catalytic conversion of methanol to aromatics, comparing with conventional HZSM-5. It is expected that the synthesis approach demonstrated here will be applicable to other zeolites with particular textural properties and controllable particle sizes, facilitating the emergence of new-type porous materials and their related applications in catalysis and separation.

Cu-based metal–organic framework/activated carbon composites for sulfur compounds removal

MOF-199 was modified by incorporating activated carbon (AC) during its synthesis under hydrothermal conditions to improve its performance in the removal of hydrogen sulfide (H2S) and dimethyl sulfide (CH3SCH3). A variety of different characterization techniques including X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, nitrogen adsorption/desorption isotherms, scanning electron microscopy (SEM), pyridine adsorption infrared spectroscopy (Py-IR), thermogravimetric- mass spectroscopy (TG-MS) and X-ray photoelectron spectroscopy (XPS) were used to analyze the fresh and exhausted composites. It was found that the composites, which have an amount of AC of less than 2%, had the same morphology as those of pristine MOF-199, but exhibited a more ordered crystallinity structure as well as higher surface area. The composite with 2% AC incorporation showed highest sulfur capacity of 8.46 and 8.53% for H2S and CH3SCH3, respectively, which increased by 51 and 41% compared to that of MOF-199. This improvement was attributed to the formation of more micropores and especially the increased number of unsaturated copper metal sites, as revealed by Py-IR. It is suggested the chemical reaction was apparent during adsorption of H2S, which resulted in the formation of CuS and the collapse of the MOF structure. Whereas reversible chemisorption was found for CH3SCH3 adsorption, as testified by TG-MS and fixed-bed regeneration. Exhausted MAC-2 can be almost totally regenerated by high temperature 180°C nitrogen purge, indicating a promising adsorbent for CH3SCH3 removal.

Al-MCM-41 supported palladium catalyst for methane combustion: Effect of the preparation methodologies

This work aimed at elucidating the beneficial effect of plasma treatment on the catalytic performance of palladium (Pd) catalysts in methane combustion with the ordered mesoporous molecular sieve Al-MCM-41 as the model support. The plasma treated Pd/Al-MCM-41 catalyst exhibited a higher initial activity and a better stability in comparison with the untreated counterpart catalyst. To clarify the plasma effect, the catalysts were characterized by N2 sorption analysis, X-ray diffraction (XRD), temperature-programmed desorption of ammonia (NH3-TPD), pyridine adsorption-infrared spectroscopy (Py-IR), high resolution-transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (CH4-TPR) experiments. The results obtained confirmed that palladium oxide (PdO) was the active phase. Plasma treatment enhanced the acidity of catalyst and improved the dispersion of PdO particles, which lead to a higher initial activity. The better stability for plasma treated Pd-based catalyst was proved to be closely related to the stronger interaction between palladium oxide and the molecular sieve support. In addition, the sintering of PdO particles over the plasma treated catalyst was not significant during the stability test. These findings may provide useful guidelines for further catalyst design for methane combustion.