Sequential Impregnation Research Articles

Interface-directed epitaxially growing nickle ensembles as efficient catalysts in dry reforming of methane

Supported nickel catalysts are promising candidates for dry reforming of methane, but agglomeration of Ni0 and coke deposition hinder the industrial applications. Herein, we report a novel interface-directed synthetic approach to construct distinct metal ensembles by carefully tuning the compositions of the carriers. A Zr-Mn-Zn ternary oxide-supported Ni catalyst, together with the respective binary oxide-supported analogues, was synthesized by adopting a sequential co-precipitation and wetness impregnation method. Combined characterization techniques identify distinct catalyst models, including (i) conventional NiO nanoparticles with different sizes on Zr-Mn and Zr-Zn, and (ii) epitaxially growing NiO ensembles of a few nanometers thickness at the periphery of MnZnOx particles. These catalysts exhibit divergent responses in the catalytic testing, with the ternary oxide system significantly outperforming the binary analogues. The strong electronic interactions between Mn-Ni increase Ni dispersion and the activity while the stability is strengthened upon Zn addition. Both high activity, high selectivity, and remarkable stability are attained upon co-adding Mn and Zn. The interfaces between Ni and Zr-Mn-Zn rather than the physical contacts of individual oxide-supported analogues through mechanical mixing are keys for the outstanding performance.

Surface structure modulating of Ni-Pt bimetallic catalysts boosts n-dodecane steam reforming

Surface structure of bimetallic catalysts plays a vital role in converting liquid hydrocarbon fuels to on-site H2 for fuel cell application via steam reforming process. Herein, Pt-outer (Pt-Ni/Al2O3), Pt-outer & inner (NiPt/Al2O3) and Pt-inner (Ni-Pt/Al2O3) catalysts prepared through sequential impregnation and co-impregnation method were employed in n-dodecane steam reforming. Performance results showed that the activity was as followed: Ni-Pt/Al2O3 > NiPt/Al2O3 > Pt-Ni/Al2O3. Characterization results from XRD, H2-TPR, XPS, STEM-EDX, in situ CO-DRIFT and EXAFS suggest that Ni-Pt/Al2O3 catalyst was more preferable to form Nix+ species and NiPt alloy compared with Pt-Ni/Al2O3 and NiPt/Al2O3 catalysts. C2H6-TPSR and H2O-TPSR experimental indicated that Ni-Pt/Al2O3 catalyst and Nix+ species mostly contributed to CC, CH bond and H2O activation. The superior activity of Ni-Pt/Al2O3 bimetallic catalyst in n-dodecane steam reforming linked with the synergistic effect between Ni-enriched surface, Nix+ species and NiPt alloy which facilitated CHx group formation, H2O activation and CHx group oxidation.

Hydrogen Production through Autothermal Reforming of Ethanol: Enhancement of Ni Catalyst Performance via Promotion

Autothermal reforming of bioethanol (ATR of C2H5OH) over promoted Ni/Ce0.8La0.2O1.9 catalysts was studied to develop carbon-neutral technologies for hydrogen production. The regulation of the functional properties of the catalysts was attained by adjusting their nanostructure and reducibility by introducing various types and content of M promoters (M = Pt, Pd, Rh, Re; molar ratio M/Ni = 0.003–0.012). The composition–characteristics–activity correlation was determined using catalyst testing in ATR of C2H5OH, thermal analysis, N2 adsorption, X-ray diffraction, transmission electron microscopy, and EDX analysis. It was shown that the type and content of the promoter, as well as the preparation mode (combined or sequential impregnation methods), determine the redox properties of catalysts and influence the textural and structural characteristics of the samples. The reducibility of catalysts improves in the following sequence of promoters: Re < Rh < Pd < Pt, with an increase in their content, and when using the co-impregnation method. It was found that in ATR of C2H5OH over bimetallic Ni-M/Ce0.8La0.2O1.9 catalysts at 600 °C, the hydrogen yield increased in the following row of promoters: Pt < Rh < Pd < Re at 100% conversion of ethanol. The introduction of M leads to the formation of a NiM alloy under reaction conditions and affects the resistance of the catalyst to oxidation, sintering, and coking. It was found that for enhancing Ni catalyst performance in H2 production through ATR of C2H5OH, the most effective promotion is with Re: at 600 °C over the optimum 10Ni-0.4Re/Ce0.8La0.2O1.9 catalyst the highest hydrogen yield 65% was observed.

Hydrodeoxygenation of guaiacol over BEA supported bimetallic Ni-Fe catalysts with varied impregnation sequence

BEA supported Ni-Fe catalysts, prepared by various impregnation techniques, were characterised and examined for their activity for the hydrodeoxygenation (HDO) of guaiacol and hydrogenation of toluene. The aim of the study was to explore the factors affecting the formation of Ni-Fe active species and explore the relationship between the concentration of surface Ni, Ni-Fe species and HDO activity. Catalysts prepared initially with Fe, or co-currently with Fe and Ni exhibited a higher level of HDO rate compared to catalyst that was prepared with Ni initially. When a catalyst was impregnated initially with Fe, metal-supported interaction was relatively weak, thus the formation of Ni-Fe species was promoted. In contrast, a reduced number of Ni sites was involved in the formation of Ni-Fe species when the catalyst was initially impregnated with Ni, resulting in a low HDO rate. The rate of cyclohexane formation is proportional to the concentration of surface Ni-Fe over the catalysts with similar Ni and Fe loadings but prepared by different impregnation sequences. The enhanced HDO rate is attributed to the hydrogenolysis activity of Ni-Fe species. The effect of Ni/Fe ratio on HDO activity was also investigated under differential conditions and the catalyst with a Ni/Fe mass ratio of 3.3 exhibited the highest rate of cyclohexane formation.

The Effect of ZrO2 as Different Components of Ni-Based Catalysts for CO2 Reforming of Methane and Combined Steam and CO2 Reforming of Methane on Catalytic Performance with Coke Formation

The role of ZrO2 as different components in Ni-based catalysts for CO2 reforming of methane (CRM) has been investigated. The 10 wt.% Ni supported catalysts were prepared with ZrO2 as a support using a co-impregnation method. As a promoter (1 wt.% ZrO2) and a coactive component (10 wt.% ZrO2), the catalysts with ZrO2 were synthesized using a co-impregnation method. To evaluate the effect of the interaction, the Ni catalyst with ZrO2 as a coactive component was prepared by a sequential impregnation method. The results revealed that the activity, the selectivity, and the anti-coking ability of the catalyst depend upon the ZrO2 content, the Ni-ZrO2 interaction, basicity, and oxygen mobility of each catalyst resulting in different Ni dispersion and oxygen transfer pathway from ZrO2 to Ni. According to the characterization and catalytic activation results, the Ni catalyst with low ZrO2 content (as a promoter) presented highest selectivity toward CO owning to the high number of weak and moderate basic sites that enhance the CO2 activation-dissociation. The lowest activity (CH4 conversion ≈ 40% and CO2 conversion ≈ 39%) with the relatively high quantity of total coke formation (the weight loss of the spent catalyst in TGA curve ≈ 22%) of the Ni catalyst with ZrO2 as a support is ascribed to the lowest Ni dispersion due to the poor Ni-ZrO2 interaction and less oxygen transfer from ZrO2 to the deposited carbon on the Ni surface. The effect of a poor Ni-ZrO2 interaction on the catalytic activity was deducted by decreasing ZrO2 content to 10 wt.% (as a coactive component) and 1 wt.% (as a promoter). Although Ni catalysts with 1 wt.% and 10 wt.% ZrO2 provided similar oxygen mobility, the lack of oxygen transfer to coke during CRM process on the Ni surface was still indicated by the growth of carbon filament when the catalyst was prepared by co-impregnation method. When the catalyst was prepared by a sequential impregnation, the intimate interaction of Ni and ZrO2 for oxygen transfer was successfully developed through a ZrO2-Al2O3 composite. The interaction in this catalyst enhanced the catalytic activity (CH4 conversion ≈ 54% and CO2 conversion ≈ 50%) and the oxygen transport for carbon oxidation (the weight loss of the spent catalyst in TGA curve ≈ 7%) for CRM process. The Ni supported catalysts with ZrO2 as a promoter prepared by co-impregnation and with ZrO2 as a coactive component prepared by a sequential impregnation were tested in combined steam and CO2 reforming of methane (CSCRM). The results revealed that the ZrO2 promoter provided a greater carbon resistance (coke = 1.213 mmol·g−1) with the subtraction of CH4 and CO2 activities (CH4 conversion ≈ 28% and CO2 conversion ≈ %) due to the loss of active sites to the H2O activation-dissociation. Thus, the H2O activation-dissociation was promoted more efficiently on the basic sites than on the vacancy sites in CSCRM.

Front Cover: Propane Aromatization Tuned by Tailoring Cr Modified Ga/ZSM‐5 Catalysts (ChemCatChem 16/2021)

The Front Cover shows a symbolic rocket. The main structure of the rocket represents ZSM-5 zeolite, and the boosters represent the added Ga and Cr species, respectively. This picture means that propane is rapidly converted into propene and hydrogen on Ga and Cr modified ZSM-5 zeolite, and then converted into BTX aromatics. In their Full Paper, B. Xu et al. introduced Cr to Ga/ZSM-5 catalyst by tuning the impregnation sequence and amount. Plenty of Cr3+ species and strong interaction between Ga species and ZSM-5 promoted the propane dehydrogenation. More propene was preferred to be produced and were further converted into BTX. More information can be found in the Full Paper by B. Xu et al.

Sequential impregnation and sol-gel synthesis of Fe-ZnO over hydrophobic silica aerogel as a floating photocatalyst with highly enhanced photodecomposition of BTX compounds from water

Benzene, Toluene, and Xylene (BTX) are included in the floating contaminants which originated from the explosion of oil wells. Photocatalytic oxidation of the some oil spill components like Benzene, Toluene, and Xylene can be a proper way to solve this challenge due to its economic saving, usage of free energy, and environmentally friendly. For this purpose, we have synthesized a hydrophobic catalyst of Fe-ZnO nanoparticles inoculated with silica aerogel (SA). Various percentage of hydrophobic silica aerogel (10, 20 and 30%) was added, as support of catalyst, to Fe-ZnO nanoparticles using impregnation method. The impregnation of silica aerogel to Fe-ZnO nanoparticles caused the photocatalytic performance of nanocatalyst was improved through its increased surface area, and also floated active phase (Fe-ZnO) on water. In order to investigate the impact of the synthetic method of nanocomposite on the activity of synthesized nanophotocatalyst, optimum samples (Fe-ZnO over 20% SiO2) were synthesized using the sol-gel method. The synthesized nanophotocatalysts were characterized using PXRD, FESEM, EDX, UV–Vis, Contact Angle, FT-IR, and BET-BJH analyses. Photocatalytic activity of synthesized nanophotocatalyst was evaluated in the degradation of the BTX after 120 min, under visible light irradiation. In addition, the influence of various parameters including the addition of hydrophobic silica aerogel, pH, catalyst loading, benzene concentration, and reusability was studied on the photodegradation efficiency of Fe-ZnO/SA (20%). The most photocatalytic activity was observed in the optimum condition involving pH = 5, catalyst loading = 1 g/L, and benzene concentration = 5% V/V.

Propane Aromatization Tuned by Tailoring Cr Modified Ga/ZSM‐5 Catalysts

AbstractAccelerating propane dehydrogenation in propane aromatization is vital because it is the first and rate control step. In this study, we introduced Cr to Ga/ZSM‐5 by tuning its impregnation sequence and amount, which was expected to accelerate the dehydrogenation step and improve aromatization performance. The impregnation sequence of Cr on catalyst not only affected the interaction between Ga and ZSM‐5, but also tuned the amount of dehydrogenation active species Cr3+. Due to the plenty of Cr3+ species and strong interaction between Ga species and ZSM‐5, 2Cr/GaZ5 catalyst accelerated the dehydrogenation step and improved the aromatization process. More light hydrocarbons were preferred to be produced and were further converted into BTX on 2Cr/GaZ5 catalyst. Excessive Cr on catalyst caused the formation of Cr2O3 particles with worse dispersion. The aggregated Cr2O3 decreased the strong acidity of catalyst, which could not further promote propane conversion and decreased the aromatization ability of catalyst.

A comparison of Structure–Activity of Cu-Modified Over Different Mesoporous Silica Supports for Catalytic Conversion of Levulinic Acid

Catalytic hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was investigated over four different types of mesoporous silica (SBA-15, MCM-48, MCM-41, and KIT-6) supported copper (5 wt.%) catalysts. The Cu was incorporated into mesoporous silica supports by a sequential impregnation method. A detailed investigation of the support structure–activity correlation and the performance of the catalysts in LA conversion was studied. Detailed characterisation techniques were used to evaluate the physical and catalytic properties of the studied catalysts. The structure type and physicochemical properties of the silica support had a significant effect on the overall performance of the catalysts. Among them, over Cu/SBA-15 catalyst, a complete levulinic acid (LA) conversion with ~ 98% gamma valerolactone (GVL) selectivity was achieved at 265 °C under ambient H2 pressure. The superior performance of Cu/SBA-15 catalyst was attributed to the high surface acidity, reducibility of Cu oxides species, and highly dispersed Cu particles over SBA-15 structure. The results confirmed that the activity of the catalysts is significantly influenced by the textural properties, surface acidity and copper dispersion. Durability of all the catalysts were also tested for 50 h time on stream and over SBA-15 catalyst, only a small drop in the activity was observed.

Ni, Mo-containing catalysts for the single-step synthesis of propylene from ethylene: the effect of the support nature

Polyfunctional Ni, Mo-containing catalysts were synthesized by sequential impregnation of the support (SiO2, Al2O3, B2O3-Al2O3, SO42–/Al2O3,SO42–/ZrO2) with solutions of the corresponding salts with intermediate drying at 120 °C and calcination at 500–550 °C. Physicochemical properties of the synthesized catalysts were studied by XRD, H2-TPR, UV-vis spectroscopy and EPR; the catalysts were tested in the singlestep synthesis of propylene from ethylene at atmospheric pressure, temperature 200 °С, and ethylene mass flow rate 0.5 h–1. The maximum values of ethylene conversion and propylene yield were observed for the sample synthesized from borate-containing alumina; this is related to the formation of active sites of ethylene dimerization – the Ni2+ cations bound to acid sites of the support, and active sites of metathesis – the surface monomolybdate compounds.

Greenhouse gas mitigation and hydrogen generation via enhanced ethylene glycol dry reforming on La-promoted Co/Al2O3 catalyst

The first investigation of La-promoted Co/Al2O3 catalysts in Ethylene Glycol-CO2 conversion (EGCC) for syngas (H2 + CO) production was conducted in this work. Co/Al2O3 catalysts modified with different La promoter loadings (1, 3, and 5%) were generated through sequential incipient wetness impregnation technique and employed for EGCC. The physicochemical attributes of the generated catalysts were examined via Brunauer-Emmett-Teller (BET), H2 temperature-programmed reduction (H2-TPR), X-ray diffraction (XRD), Raman, and temperature-programmed oxidation (TPO). 3%La-promoted catalyst owned the largest specific surface area, smallest Co crystallite size of 9.8 nm, and lowest reduction temperature among the promoted catalysts. These excellent properties resulted in the highest catalytic performance on the 3%La-promoted catalyst (i.e., C2H6O2 conversion = 77.6 %, CO2 conversion = 43.1 %, H2 yield = 75.3 %, and CO yield = 76.8 %). The significant reduction in carbon deposition of the 3%La-promoted catalyst was due to the La capability in eliminating deposited carbon via the formation of intermediate lanthanum dioxycarbonate, La2O2CO3.

Hydrogen Production From Steam Gasification of Palm Kernel Shell Using Sequential Impregnation Bimetallic Catalysts

Zeolite β supported bimetallic Fe and Ni catalysts have been prepared using sequential impregnation method and calcined at temperatures between 500-700 ºC. The catalytic activity of these catalysts in a steam gasification of palm kernel shell was tested in a fixed-bed quartz micro-reactor at 700 ºC. Both Fe and Ni active metals present in FeNi/BEA and NiFe/BEA catalysts are corresponding to Fe2O3 and NiO. Different calcination temperatures and different sequence in metal addition have a significant effect to the catalytic activity where FeNi/BEA (700) shows the highest hydrogen produced than other catalysts.

Effect of impregnation sequence of Cr on steaming reforming of methanol to hydrogen over CuO-CeO2 catalysts

Effect of impregnation sequence of Cr on steaming reforming of methanol to hydrogen over CuO-CeO2 catalysts

Effect of drying rate on the performance of Pt-Sn-K/γ-Al2O3 catalyst for propane dehydrogenation

The dehydrogenation of propane to propylene over Pt-Sn-K/γ-Al2O3 catalysts prepared by sequential impregnation was studied. Three drying rates, that is, 5, 10 and 15 °C/min were applied after incipient wetness impregnation of the support (1.6–1.8 mm in diameter) with KNO3. The obtained catalysts were characterized by N2 physisorption, SEM-EDAX analysis and XRF for textural and chemical properties. Catalytic performance tests were performed in a fixed-bed quartz reactor under kinetically controlled conditions for proper catalyst screening. The EDAX measurement results illustrated that the potassium concentration profile changed with drying rate with the catalyst prepared by lower drying rate exhibited highest K concentration at the center as well as highest propylene yield. These were attributed to the retraction of impregnation solution during drying at slow rates which results in lower concentration of acidic sites in catalyst center, thereby reducing the contact time of the propylene product with strong acid sites during reaction.

The Effect of Addition Method of Impregnation Solution on Properties and Performance of Pd-Ag/Al2O3 Catalyst in Tail-End Acetylene Selective Hydrogenation

The impregnation of alumina support with PdCl2 solution was investigated in batch and semi-batch operation modes using a recycle packed-bed reactor. UV-visible analysis was used to evaluate the kinetics of Pd adsorption on alumina support. Transient palladium adsorption data showed that Pd adsorption was very rapid completing within few minutes. Bi-metallic Pd-Ag/Al2O3 catalysts were synthesized by sequential impregnation method. CO-chemisorption, CO-TPD and FE-SEM tests were used to characterize the synthesized bi-metallic samples. Catalytic performance of the samples was evaluated for tail-end acetylene selective hydrogenation process in a fixed-bed reactor. Moreover, the deactivation of the catalysts was evaluated mathematically by integral method of analysis, considering reaction kinetics as power laws in terms of nth orders in H2 and C2H2 partial pressures. It was observed that by batch-wise addition of Pd precursor solution, a sample was obtained with lowest amount of Pd dimmers that had highest ethylene selectivity and lowest hydrogenation reaction rate.

Sequentially prepared Mo-V-Based SCR catalyst for simultaneous Hg0 oxidation and NO reduction

Molybdenum (Mo)-vanadium (V)-based selective catalytic reduction (SCR) catalyst synthesized by the sequential impregnation of Mo and W followed by V was investigated for simultaneous elemental mercury (Hg0) oxidation and nitrogen oxide (NO) reduction in an existing SCR unit with respect to different TiO2 phases, calcination temperatures, flue gas constituents, gas velocities, and reaction temperatures. Anatase phase TiO2 and the calcination temperatures of 400 and 500 °C resulted in ∼69% Hg0 oxidation at 10 ppmv HCl and 350 °C. The high calcination temperature of 700 °C resulted in TiO2 phase transformation from anatase to rutile and agglomeration. The modified SCR catalyst prepared with the impregnation sequence of Mo and W followed by V using anatase TiO2 and calcination temperature 500 °C showed ∼99% Hg0 oxidation and 87% NO reduction conversions at an NH3/NO molar ratio of 0.9 under 350 °C and 5,000 hr−1 space velocity in typical sub-bituminous and lignite coal simulated flue gases. The effects of these parameters and conditions were further investigated using various characterization techniques including BET, TEM, XRD, NH3 TPD and XAFS.

Novel hybrid method to additively manufacture denser graphite structures using Binder Jetting

This study introduces two hybrid processes integrating an additive manufacturing technique with post-processing treatments namely (i) Binder Jetting Printing (BJP) + Cold Isostatic Pressing (CIP) + cycle and (ii) BJP + cycle where cycle refers to a sequence of Impregnation—Drying—Pyrolysis. These two new processes yielded additively manufactured parts with higher density and reduced defects/porosities. As a testbed, we used these new processes to fabricate graphite structures. The samples produced by both methods were compared with each other and benchmarked to the samples produced by (a) BJP alone and (b) Traditional uniaxial pressing like compaction moulding. Various characterisation methods were used to investigate the microstructure and mechanical properties which showed that the porosity of hybrid manufactured samples reduces from 55% to a record 7%. This technological pathway is expected to create a new avalanche of industrial applications that are hitherto unexplored in the arena of hybrid additive manufacturing with BJP method.

NiMo carbide supported on algal derived activated carbon for hydrodeoxygenation of algal biocrude oil

The use of novel algae-derived activated carbon supported NiMo carbide catalysts for upgrading algal biocrude oil by hydrodeoxygenation was investigated. The carbide catalysts were prepared in a two-step process involving sequential impregnation or co-impregnation of NiMo on activated carbon and followed by carbonization through three different methods namely temperature-programmed reaction with 20%CH4-80%H2, carbothermal hydrogen reduction in H2, and carbothermal reduction in N2. The synthesized carbide catalysts were characterized using XRD, BET, TPD-NH3, TGA, and XPS techniques. The catalysts were screened for hydrodeoxygenation (HDO) of algal biocrude at various process conditions in a stirred tank reactor to produce liquid hydrocarbon fuels. The liquid hydrocarbon product was analyzed by 1HNMR, 13CNMR, Sim-dist, CHNS, and GC–MS to gain insight into algal biofuel properties. The NiMo carbide synthesized through co-impregnation and carbothermal reduction in N2 showed optimal activity for oxygen removal due to its high acidity and specific surface area and a greater amount of Mo2C as active phases on the surface. Response surface methodology was applied for NiMoC catalyst to optimize the effects of temperature (350–450 °C), catalyst loadings (5–15 wt%), and reaction time (1.5–4 h) at a constant pressure of 3 MPa. The upgraded biocrude oil revealed an oxygen reduction percentage of 94% with HHV of 43.9 MJ/kg.

The catalytic activity of microporous and mesoporous NiCoBeta zeolite catalysts in Fischer–Tropsch synthesis

Two kinds of microporous and mesoporous NiCoBeta zeolite catalysts were prepared. The effect of bimetallic zeolite preparation method, dealumination degree, the presence of micropores in the support structure and the effect of nickel addition on the activity and selectivity of cobalt-based microporous and mesoporous dealuminated and non-dealuminated zeolite catalysts in Fischer–Tropsch synthesis were determined. These catalysts were obtained by sequential impregnation (Ni3.0Co20AlBeta and Ni3.0Co20SiBeta) and co-impregnation (co-Ni3.0Co20AlBeta and co-Ni3.0Co20SiBeta). The study showed that the presence of Ni leads to a lower cobalt oxide reduction temperature and an increase in CO conversion. Nickel–cobalt zeolite systems showed high activity and selectivity throughout the lifetime of the reaction. The use of a two-step post-synthesis method and the promotion of cobalt systems with nickel allow to obtain active, selective, and stable zeolite catalysts for Fischer–Tropsch synthesis.

CeO2-Promoted Ni/SiO2 Catalysts for Carbon Dioxide Reforming of Methane: The Effect of Introduction Methodologies

Three typical methods, subsequent coating, co-impregnation and sequential impregnation, were employed to investigate the effect of introduction methodologies for CeO2-promoted Ni/SiO2 catalysts. The CeO2@Ni/SiO2 catalyst prepared with the subsequent coating method was found to exhibit the best initial activity and superior long-term stability in CO2 reforming of methane. Comparative characterizations documented that small Ni size and intimate Ni–CeO2 contact were generated on the CeO2@Ni/SiO2 catalyst, leading to excellent reforming activity. In addition, pronounced redox property and strong surface basicity were created on the CeO2@Ni/SiO2 catalyst, resulting in exceptional coke resistance and thus superior long-term stability. This work unravels the impact of various introduction methods on the catalyst structure, which would help design robust nanocomposite catalysts with outstanding catalytic performance.