Temperature-programmed Reduction Method Research Articles

Temperature-programmed reduction method for stabilization of the inorganic framework of SAPO-37 materials: promising catalysts for MTBE production.

A temperature-programmed reduction method was developed to stabilize SAPO-37 and molybdenum-(oxy)-carbide-loaded SAPO-37 (SAP-37MoCR). The inorganic framework (Faujasite type SAPO-37) was retained for the first time even after treatment at 550 °C and was confirmed through powder XRD and SEM analysis. SAP-37MoCR exhibits strong acidic sites and is a promising catalyst for MTBE synthesis. Furthermore, the catalyst is stable and recyclable.

Modifying the active phase structure of Ni2P/Al2O3 by Ga introduction for improved hydrodesulfurization of diesel

Modifying the structure of active phase is an effective protocol to improve the catalytic activity of hydrodesulfurization (HDS) catalyst. Here, a variety of mesoporous GaAlOx supports with various Ga doping amount were synthesized by a facile hydrothermal strategy. The corresponding Ni2P supported catalysts were fabricated via a conventional impregnation and temperature-programmed reduction method, and their catalytic performances for 4,6-DMDBT HDS were examined. The experimental analyses show that the introduction of Ga substantially influences the geometric and electrical structure of Ni2P active phase on Ni2P/GaAlOx catalysts. The metal-support interaction is effectively abated with the elevation of Ga doping amount, thereby increasing the d-electron density of Ni species and boosting the pre-hydrogenation (HYD) route, thereupon enhancing the HDS performances of corresponding Ni2P/GaAlOx catalysts. Therein, Ni2P/GaAlOx-0.50 exhibits the highest activity with 70.1% 4,6-DMDBT conversion because of the optimal morphology and percentage of active phase, as well as distinguished redox and acid property. Further increasing the Ga loading, however, inhibits the HDS activity of Ni2P/GaAlOx-1.0 catalyst due to the decrease in the fraction and dispersion of active phases. Therefore, this work may shine light on the understanding of structure–activity of HDS catalyst and thereafter the preparation of HDS catalysts with high efficiency in future.

Optimization of Ni/ZnZr catalyst for enhanced syngas yield in catalytic pyrolysis of rice straw

To enhance the catalytic performance of nickel-based catalysts and improve their efficiency in biomass pyrolysis, a nickel-based catalyst supported on a ZnZr composite carrier was synthesized using the sol-gel method. The morphological changes of the catalyst before and after the reaction were observed using X-ray diffraction, scanning electron microscopy, nitrogen gas adsorption, temperature-programmed reduction, and other methods to analyze its catalytic performance. A series of experiments were conducted to explore the optimal conditions for the catalyst’s gas production, including carrier material ratios, loading amounts, residence time, and reaction temperature. The bimetallic carrier of Zn and Zr provided a higher specific surface area, allowing the metallic nickel to enter its mesopores. The synergistic effect of the bimetallic system facilitated the catalytic activity of nickel, significantly enhancing gas production. The maximum CO and H2 production were achieved at Zn/Zr = 6/4. The catalyst achieved an optimal gas yield of 507 mL/g at a residence time of 20 min and a reaction temperature of 800 °C, demonstrating strong stability.

Synthesis and Characterization of Supported Mixed MoW Carbide Catalysts.

For mixed MoW carbide catalysts, the relationship between synthesis conditions, evolution of (mixed) phases, extent of mixing, and catalytic performance of supported Mo/W carbides remains unclear. In this study, we prepared a series of carbon nanofiber-supported mixed Mo/W-carbide catalysts with varying Mo and W compositions using either temperature-programmed reduction (TPR) or carbothermal reduction (CR). Regardless of the synthesis method, all bimetallic catalysts (Mo:W bulk ratios of 1:3, 1:1, and 3:1) were mixed at the nanoscale, although the Mo/W ratio in individual nanoparticles varied from the expected bulk values. Moreover, the crystal structures of the produced phases and nanoparticle sizes differed depending on the synthesis method. When using the TPR method, a cubic carbide (MeC1-x ) phase with 3-4 nm nanoparticles was obtained, while a hexagonal phase (Me2C) with 4-5 nm nanoparticles was found when using the CR method. The TPR-synthesized carbides exhibited higher activity for the hydrodeoxygenation of fatty acids, tentatively attributed to a combination of crystal structure and particle size.

Advanced high-iron coal fly ash zeolites for low-carbon emission catalytic combustion of VOCs

Coal fly ash zeolites (CFAZs) with increased iron oxide content were prepared by double-stage alkaline conversion of high-iron lignite coal ash. Catalysts were modified by applying radiofrequency plasma treatment with trifluoromethane (RF CHF3) to increase their surface activity. Textural, compositional, and structural characterization of the parent and plasma-modified zeolites were performed by N2-physisorption, X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FT-IR) spectroscopy. Oxidation state and coordination of iron species were studied by Mössbauer spectroscopy, UV-Vis spectroscopy and temperature-programmed reduction method (TPR). Acidic properties were investigated by FT-IR spectroscopy of adsorbed pyridine. The initial and plasma-modified samples were studied under toluene oxidation, where toluene was used as a model VOC. The plasma-modified iron-enriched zeolite was found to exhibit high catalytic activity for VOC oxidation, reaching a 98% toluene conversion rate at 500 °C. Despite some structural degradation effects, the plasma-treated catalysts outperformed the untreated ones in catalytic activity. Furthermore, CO2 adsorption capacity of the plasma-modified zeolite was investigated under dynamic conditions. Although plasma-treated iron-enriched zeolite showed relatively low specific surface area (194 m2/g), high dynamic carbon capture capacity of 3.8 mmol/g was measured. It significantly exceeded the capacity of CFAZs with higher specific surface area, not to mention the pure zeolite phase.

Preparation of ultrasmall Ni2P nanoparticles with low P/Ni ratios supported on SiO2 and an Al2O3-B2O3 mixed oxide for dibenzothiophene hydrodesulfurization

Ultrasmall Ni2P nanoparticles with dimensions around 3 ∼ 5 nm supported on SiO2 (Ni-P/SiO2) and an Al2O3-B2O3 mixed oxide (Ni-P/AB) were prepared by a temperature-programmed reduction method using mixtures of Ni(NO3)2 and H3PO3 as precursors. The minimum P/Ni ratios of the precursors needed for the formation of phase-pure Ni2P on SiO2 and Al2O3-B2O3 were as low as 0.8 and 0.7, respectively. The introduction of B2O3 to γ-Al2O3 inhibited the formation of AlPO4 during the reduction process. For such small particles, the effect of Ni2P-support interaction became significant, resulting in different properties of the Ni-P/SiO2 and Ni-P/AB catalysts as well as different performances in the hydrodesulfurization of dibenzothiophene. The ultrasmall Ni2P nanoparticles in the Ni-P/SiO2 catalysts that possess weak Ni2P-support interaction were as active as large Ni2P particles on SiO2 and a macro-mesoporous Al2O3. These catalysts were one order of magnitude more active than the Ni-P/AB catalysts with strong Ni2P-support interaction.

Enhancement of commercial ZnO adsorption and photocatalytic degradation capacity of methylene blue by oxygen vacancy modification: Kinetic study

The effect of the introduction of oxygen vacancies on commercial ZnO by hydrogen reduction on the adsorption and photocatalytic degradation of methylene blue is investigated. Commercial ZnO was reduced at 500 °C by a 10% H2/Ar gas with a temperature programmed reduction method. Both pristine and reduced photocatalysts were characterized by TPR, FE-SEM, EDS, XPS, XRD, BET, and PL analyses. The bandgap of the photocatalysts was estimated by Tauc plot method. The characterization results indicated that the morphology and crystallinity of the nanoparticles remained unchanged after the reduction treatment, while the ratio of the oxygen vacancy to the lattice oxygen was increased. Furthermore, the maximum valence band of the photocatalyst experienced an upward shift from 2.43 to 2.67 eV which resulted in a decrease of the bandgap from 3.22 eV in commercial ZnO to 3.07 eV in the reduced photocatalyst. To investigate the effect of hydrogen reduction on the adsorption in the dark and photocatalytic degradation of methylene blue, experiments were performed using both commercial and reduced photocatalysts at a pH range between 3 and 11. Our recently developed kinetic model, taking into account non-equilibrium adsorption and photocatalytic degradation via radicals (in solution) and electron-holes (at the photocatalyst surface), was used to describe the experimental data. The results showed that the concentration of active sites of the photocatalyst increased by ∼ 20% after the hydrogen reduction, resulting in higher adsorption and photocatalytic degradation. The highest adsorption takes place at pH 3, while the degradation rate and quantum yield reach their maximal value at pH 11. Finally, the definition of quantum yield is revisited in terms of actual degradation, rather than liquid concentration differences.

Hydrodeoxygenation–Isomerization of Methyl Palmitate over SAPO-11-Supported Ni-Phosphide Catalysts

Ni-phosphide catalysts on SAPO-11 were studied in the hydrodeoxygenation–isomerization of methyl palmitate (C15H31COOCH3—MP). The catalysts were synthesized using temperature-programmed reduction (TPR) of a phosphate precursor ((NH4)2HPO4 and Ni(CH3CH2COO)2), TPR of a phosphite precursor (H3PO3 and Ni(OH)2), and using phosphidation of Ni/SAPO-11 by PPh3 in the liquid phase. The samples were characterized by ICP-AES chemical analysis, N2 physisorption, NH3-TPD, XRD, and TEM. First, the screening of the catalysts prepared by the TPR method was carried out in a semi-batch autoclave to determine the influence of the preparation method and conditions on one-pot HDO–isomerization (290–380 °C, 2–3 MPa). The precursor’s nature and the amount of phosphorus strongly influenced the activity of the catalysts and their surface area and acidity. Isomerization occurred only at a low P content (Ni/P = 2/1) and blocking of the SAPO-11 channels by unreduced phosphates at higher P contents did not allow us to obtain iso-alkanes. Experiments with liquid phosphidation samples in a continuous-flow reactor also showed the strong dependence of activity on phosphidation duration as well as on Ni content. The highest yield of isomerized products (66% iso-C15–16 hydrocarbons, at complete conversion of O-containing compounds, 340 °C, 2 MPa, and LHSV = 5.3 h−1) was obtained over 7% Ni2P/SAPO-11 prepared by the liquid phosphidation method.

Bimetal defects boost efficient photocatalytic H2O2 in-situ production of Cu1-xCo2-yO4-z for contaminant degradation

Targeted design of metal defects in photocatalysts helps to realize stable and efficient wastewater treatment. Herein, a novel spinel Cu1-xCo2-yO4-z with bimetal defects is precisely designed by a simple temperature programmed reduction method in hydrogen atmosphere. The co-existence of metallic defects leads to defects distortion forming polarization effect, which can significantly accelerate the separation of photogenerated carriers. By optimizing the band structure, Cu1-xCo2-yO4-z induced in-situ H2O2 production (190 μmol L−1·h−1 with sacrificial agent and 78 μmol L−1·h−1 without sacrificial agent) to boost the generation of hydroxyl radical, and the photodegradation activity was 7.8 and 8.4 times for MB and Cr(VI) as that of CuCo2O4, respectively. Bimetal defects achieve high performance through in-situ production of H2O2 and purification of contaminants, providing novel strategies for the applications of spinel photocatalysts in environmental purification.

Novel gallium-based voltammetric sensor for sensitive detection of cysteine

Carbon nanotube-supported gallium (Ga/CNT) was synthesized and characterized with energy dispersive X-ray-scanning electron microscopy, temperature-programmed reduction, temperature-programmed oxidation, and temperature-programmed desorption methods. Characterization results revealed successful preparation of Ga/CNT. Electrochemical measurements were performed by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. The Ga/CNT-based cysteine sensor had a linear response within the range of 0–200 μM with current sensitivity of 0.0081 μA/μM (114 μA/mM cm2), low detection limit of 0.05 μM, and signal-to-noise ratio of 3. Interference studies revealed that (Ga/CNT)@glassy carbon electrode was not affected by interfering species. Thus, Ga/CNT is a promising cysteine sensor.

Preparation of the Nanostructured Ni-Mg-O Oxide System by a Sol-Gel Technique at Varied pH.

In the present work, a series of two-component Ni-Mg-O oxide systems were prepared using a sol–gel technique at varied pH of hydrolysis procedure. The aqueous solutions of nitric acid or ammonia were added to control the pH values. The xerogel samples obtained after drying were analysed using a thermogravimetric approach. The oxide systems were characterized by a set of physicochemical methods (low-temperature nitrogen adsorption, X-ray diffraction analysis, scanning electron microscopy, UV-vis spectroscopy, and temperature-programmed reduction method). The thermal stability of the samples was examined in a testing reaction of CO oxidation in a prompt thermal aging regime. It was revealed that the pH value during the magnesium methoxide hydrolysis stage significantly affects the properties of the intermediate hydroxide and final oxide nanomaterials. The thermal decomposition of nitric acid or ammonia is accompanied by exothermal effects, which noticeably influence the textural characteristics. Moreover, the pH of the hydrolysing solution defines the strength of the nickel interaction with the MgO matrix. An increase in pH facilitates the formation of the NixMg1−xO solid solution with a higher amount of incorporated nickel, which is characterized by the reproducible broad temperature range of the hydrogen uptake and the enhanced thermal stability.

Thermal stability and reduction mechanism of LiNi0.8Co0.1Mn0.1O2 and LiNi0.5Co0.2Mn0.3O2 cathode materials studied by a Temperature Programmed Reduction

The temperature Programmed Reduction method was applied to analyze the structural and thermal behavior of LiNixCoyMnzO2 (x = 0.5 and 0.8). All reduction phases of LiNi0.5Co0.2Mn0.3O2 powder were transitioned above 843 K. For LiNi0.8Co0.1Mn0.1O2 powder, three reduction steps are starting at 661 K. It contributes to the transition to Ni2+, Co2+, Ni0, and Co0 phases, respectively. It was consistent with the reduction mechanism of LiNiO2 and LiCoO2. In delithiated NCM523, only a structural change from H1 to M is observed, which does not significantly affect thermal stability. For delithiated NCM811, the TPR result was sharply reduced to 536 K in the H2-H3 structural transition. When charged to 4.4 V, it decomposes into a NiO-like phase at 507 K. The reducing phase was verified through X-ray diffraction after all decomposition steps of the TPR results. As a result, the TPR method can confirm the reduction mechanism and thermal stability of the cathode material.

Quasi-operando quantification of Cu(II) ions in Cu-SSZ-13 catalyst by an NH3 temperature-programmed reduction method.

A quasi-operando NH3 temperature-programmed reduction method (NH3-TPR), with N2:Cu = 1:1, is developed to quantify total Cu(ii) ions in Cu-SSZ-13 quenched from SCR-relevant reactions, and its accuracy is confirmed by in situ EPR. [Cu(OH)]+-Z and Cu2+-2Z can be further distinguished by NH3 reduction temperatures, and their different reducibility in SCR is revealed.

Bimetallic AgPd/UiO-66 Hybrid Catalysts for Propylene Glycol Oxidation into Lactic Acid.

Different methods (the wetness impregnation of Ag and Pd precursors dissolved in water or acetonitrile solution, and the double solvent impregnation technique) were employed to immobilize Ag–Pd nanoparticles (NPs) into the pores of the microporous zirconium-based metal-organic framework known as UiO-66. The obtained materials were characterized by using nitrogen adsorption-desorption at −196 °C, powder X-ray diffraction, UV-Vis diffusion reflectance spectroscopy, and transition electron microscopy measurements. Special attention was paid to the acid and redox properties of the obtained materials, which were studied by using temperature-programmed desorption of ammonia (TPD-NH3) and temperature-programmed reduction (TPR-H2) methods. The use of a drying procedure prior to reduction was found to result in metallic NPs which, most likely, formed on the external surface and were larger than corresponding voids of the metal-organic framework. The formation of Ag–Pd alloy or monometallic Ag and Pd depended on the nature of both metal precursors and the impregnation solvent used. Catalytic activity of the AgPd/UiO-66 materials in propylene glycol oxidation was found to be a result of synergistic interaction between the components in AgPd alloyed NPs immobilized in the pore space and on the external surface of UiO-66. The key factor for consistent transformation of propylene glycol into lactic acid was the proximity between redox and acid-base species.

Turning poison into medicine: NH3 or urea treatment leads to improved Pd-based three-way catalysts

Contrary to the stereotype that exposure to NH3 or urea should be strictly avoided when preparing three-way catalysts using Pd due to Pd2+-NH3 coordination, remarkable catalytic activity improvement was realized with careful NH3 or urea treatment towards the oxides support or Pd precursor. And with the help of a newly designed facile CO temperature-programmed reduction (TPR) method, developed to replace traditional H2-TPR, it was found that the catalytic activity is closely related with the catalyst reducibility and total oxygen storage capacity (OSC, represented by the integrated area of a CO-TPR curve), thus showing the potential of this CO-TPR method for screening candidate catalysts. When applying the most effective “Urea-PP” technology during monolith converter preparation, this method could no longer show its advantage, unless an outer layer was coated to protect the highly active but also highly sensitive inner layer.

Effect of preparation methods on the structure and naphthalene hydrogenation performance of Ni2P/SiO2 catalyst

Ni2P/SiO2 catalysts were prepared by temperature-programmed reduction method and hypophosphite disproportionation method to investigate their naphthalene hydrogenation performance. The prepared catalysts were characterized by ICP-OES, X-ray diffraction, H2 temperature-programmed reduction, N2 adsorption-desorption method and transmission electron microscopy, etc. Results showed that Ni2P/SiO2 catalyst with pure Ni2P crystal phase could be successfully prepared by the temperature-programmed reduction method and hypophosphite disproportionation method. When the naphthalene hydrogenation reaction was performed at 340°C, 4 MPa, H2/oil volume ratio of 600, and a weight hourly space velocity (WHSV) of 20.8 h–1, Ni2P/SiO2 catalyst prepared by the temperature-programmed reduction method possessed superior hydrogenation activity. This result was ascribed to the advantages of temperature-programmed reduction method. It not only installed the higher number of Ni2P species (CO adsorption amount 21.6 μmol/g) over SiO2, but also obtained more weak acid sites on the catalyst surface, which promoted the adsorption of aromatic hydrocarbons and subsequently resulted in the higher hydrogenation activity. Furthermore, when the temperature-programmed reduction method was used to prepare Ni2P/SiO2 catalyst, the lower Ni/P molar ratio was more beneficial to enhance the naphthalene hydrogenation activity of the as-prepared catalyst.

Reduction behavior of tungsten oxide with and without scandia doping

As an important powder material for scandate cathode, Sc2O3-doped WO3 powder together with hollow spherical WO3 for comparison was prepared by spray-drying method. The reduction behavior and kinetics of pure WO3 and Sc2O3-doped WO3 were studied by temperature-programmed reduction (TPR) method. It is found that scandia doping can decrease the reduction activation energy of WO3 and thus lower the reduction temperature and increase the reduction rate. Based on the kinetics results, the reduction techniques are presented. The obtained powder has a narrow size distribution in the range of 0.6–0.8 μm.

Nanostructured molybdenum Phosphide/N-Doped carbon nanotube-graphene composites as efficient electrocatalysts for hydrogen evolution reaction

Uniformly dispersed ∼10 nm MoP nanoparticles on N-doped carbon nanotube and graphene composite (NCNT-NGR) support are synthesized via a simple temperature-programmed reduction method for electrocatalytic hydrogen evolution reaction (HER). The NCNT-NGR support is composed of well-intercalated carbon nanotube (CNT) between graphene layers, resulting in suppressed CNT bundling and graphene re-stacking, hence providing a large surface area. The prepared MoP/NCNT-NGR composite exhibits high HER activity than control catalysts (MoP/NCNT, MoP/NGR, and bare MoP) with a small benchmark overpotential of 100 mV to drive 10 mA/cm2 and an improved Tafel slope of 44 mV/dec in an acidic medium. It also exhibits excellent stability for 1000 potential cycles and in a 10-h chronoamperometry test. Such a HER performance arises from synergy between highly active MoP nanoparticles and the large surface area/highly conductive NCNT-NGR support.

Structure and Activity of Ni2P/Desilicated Zeolite β Catalysts for Hydrocracking of Pyrolysis Fuel Oil into Benzene, Toluene, and Xylene

The effects of desilication (DS) of the zeolite β on the hydrocracking of polycyclic aromatics were investigated using the Ni2P/β catalysts. The Ni2P/β catalysts were obtained by the temperature-programmed reduction (TPR) method, and the physical and chemical properties were examined by N2 physisorption, X-ray diffraction (XRD), 27Al magic angle spinning–nuclear magnetic resonance (27Al MAS NMR), extended X-ray absorption fine structure (EXAFS), isopropyl amine (IPA) and NH3 temperature-programmed desorption (TPD), CO uptake, and thermogravimetric analysis (TGA). The catalytic activity was examined at 653 K and 6.0 MPa in a continuous fixed bed reactor for the hydrocracking (HCK) of model compounds of 1-methylnaphthalene (1-MN) and phenanthrene or a real feedstock of pyrolysis fuel oil (PFO). Overall, the Ni2P/DS-β was observed as more active and stable in the hydrocracking of polycyclic aromatics than the Ni2P/β catalyst. In addition, the Ni2P/β suffered from the coke formation, while the Ni2P/DS-β maintained the catalytic stability, particularly in the presence of large polycyclic hydrocarbons in the feed.

Ni2P/Al2O3 hydrodesulfurization catalysts prepared from hypophosphite under a nitrogen atmosphere

A novel method for preparing Ni2P/Al2O3(L) catalysts in an N2 atmosphere by decomposition of hypophosphites was proposed, and Ni2P/Al2O3(T) catalyst was synthesized by the temperature programmed reduction method in a H2 atmosphere for comparison. These prepared catalysts were washed with deionized water to remove impurities. The X-ray diffraction, N2-adsorption specific surface area measurements, CO uptake, and X-ray photoelectron spectroscopy were applied to characterize these catalysts. The activities of the Ni2P/Al2O3 catalysts prepared with the two different methods were tested in the dibenzothiophene hydrodesulfurization reaction.