Cu,Zn,Al layered double hydroxides as precursors for copper catalysts in methanol steam reforming – pH-controlled synthesis by microemulsion technique

By co-precipitation inside microemulsion droplets a Cu-based catalyst precursor was prepared with a Cu:Zn:Al ratio of 50:17:33. A pH-controlled synthesis was applied by simultaneous dosing of metal solution and precipitation agent. This technique allows for continuous operation of the synthesis and enables easy and feasible up-scaling. For comparison conventional co-precipitation was applied with the same composition. Both techniques resulted in phase pure layered double hydroxide precursors and finally (after calcination and reduction) in small Cu nanoparticles (8 nm) and ZnAl2O4. By applying the microemulsion technique smaller Cu/ZnAl2O4 aggregates with less embedded Cu particles were obtained. The microemulsion product exhibited a higher BET and specific Cu surface area and also a higher absolute catalytic activity in methanol steam reforming. However, the Cu surface area-normalized, intrinsic activity was lower. This observation was related to differences in interactions of Cu metal and oxide phase

Enhancing of catalytic properties of vanadia via surface doping with phosphorus using atomic layer deposition

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Vac. Sci. Technol. A 34, 01A135 (2016) and may be found at https://doi.org/10.1116/1.4936390.Atomic layer deposition is mainly used to deposit thin films on flat substrates. Here, the authors deposit a submonolayer of phosphorus on V2O5 in the form of catalyst powder. The goal is to prepare a model catalyst related to the vanadyl pyrophosphate catalyst (VO)2P2O7 industrially used for the oxidation of n-butane to maleic anhydride. The oxidation state of vanadium in vanadyl pyrophosphate is 4+. In literature, it was shown that the surface of vanadyl pyrophosphate contains V5+ and is enriched in phosphorus under reaction conditions. On account of this, V2O5 with the oxidation state of 5+ for vanadium partially covered with phosphorus can be regarded as a suitable model catalyst. The catalytic performance of the model catalyst prepared via atomic layer deposition was measured and compared to the performance of catalysts prepared via incipient wetness impregnation and the original V2O5 substrate. It could be clearly shown that the dedicated deposition of phosphorus by atomic layer deposition enhances the catalytic performance of V2O5 by suppression of total oxidation reactions, thereby increasing the selectivity to maleic anhydride.DFG, 53182490, EXC 314: Unifying Concepts in Catalysi

Dataset on infrared spectroscopy and X-ray diffraction patterns of Mg–Al layered double hydroxides by the electrocoagulation technique

The XRD profiles and FTIR analysis of sludge aggregates, Mg–Al layered double hydroxides, produced during electrocoagulation processes are presented. The data describes the composition of materials (LDH) produced at different operations conditions (atmospheric conditions and Mg2+/Al3+ ratio). The data show the diffraction peaks of (003), (006), (018) and (110) crystal planes for hydrotalcite structure

A Kinetic Insight into the Activation of n-Octane with Alkaline-Earth Metal Hydroxyapatites

Alkaline-earth metal hydroxyapatites are prepared by the co-precipitation method and characterized using XRD, ICP,NH3-TPD, SEM-EDX, TEM and N2 physisorption analysis. The metal present in the hydroxyapatite influences the acidity of the catalyst. Oxidative dehydrogenation reactions carried out in a continuous flow fixed bed reactor showed that the selectivity towards desired products was dependent on the alkaline-earth metal in the hydroxyapatite. All hydroxyapatite catalysts showed high selectivity towards carbon oxides, followed by cracked products, octenes and aromatics. The highest selectivity and turnover numbers towards C8 products and a high specific rate was shown by Sr-HAp. The activation of n-octane over these catalysts followed the Eley-Rideal mechanism.KEYWORDS Hydroxyapatite, acidity, chemisorption, n-octane, octenes, aromatics, oxidative dehydrogenation

A multi-function compact micro-channel reactor coated with sulphur tolerant catalyst for LPG steam reforming

Hydrogen fuelled polymer electrolyte fuel cells (PEFC) offer clear environmental benefits. Lack of viable hydrogen infrastructure in the near future means that a key issue is availability of hydrogen at the point of use. Liquefied petroleum gas (LPG) offers advantages as a fuel over other hydrocarbons because there is already an infrastructure in place for remote areas. Hydrogen supply via steam reforming of LPG is therefore a feasible avenue of achieving the environmental benefits. Commercial grade LPG unavoidably contain sulphur as an odorant, the sulphur needs to be removed from the fuel stream before it reaches the reformer catalyst and fuel cell. Utilizing sulphur tolerant catalysts in the reformer leads to a simpler fuel processor design. Thermal management and reforming efficiency has been a challenge for the sulphur tolerant catalysts. In this paper, a multi-function compact micro-channel reactor designed for hydrocarbon steam reforming was evaluated for use with LPG. A sulphur tolerant catalyst was wash-coated on to the reforming layers. The reformer was tested over a wide range of reactor temperatures, steam to carbon ratios and fuel flow rates. Over 60% of H2 composition can be achieved at high reforming temperatures with a LPG supply rate of 0.75 dm3 min−1 (STP) and a S/C ratio of 4

On mechanism of formation of SBA-15/furfuryl alcohol-derived mesoporous carbon replicas and its relationship with catalytic activity in oxidative dehydrogenation of ethylbenzene

A series of CMK-3-like carbon replicas was synthesized by precipitation polycondensation of furfuryl alcohol in an aqueous slurry of SBA-15 at a polymer/SiO2 mass ratio of 0.50–2.00. Changes in textural and structural parameters of SBA-15 after polymer deposition were studied by N2 adsorption and X-ray diffraction. Morphology of the replicas was investigated by transmission electron microscopy, while their surface composition was determined by temperature-programmed desorption and X-ray photoelectron spectroscopy. The mechanism of deposition of poly(furfuryl alcohol) (PFA) onto silica surface was elucidated. It was found that PFA accumulates in SBA-15 pores randomly; certain channels are completely filled, while others remain partially empty. The incomplete filling of mesopores results in “pseudo-CMK-3” structures featuring the bimodal porosity (the typical mesopores of CMK-3 are accompanied by broader ones formed by the coalescence of adjacent partially hollow pores). The total filling of pores with PFA leads to the formation of good-quality CMK-3. The carbon replicas exhibited the presence of abundant amounts of superficial oxygen-containing moieties. These entities are responsible for high activity of the materials in the oxidative dehydrogenation (ODH) of ethylbenzene, bringing evidence supporting the mechanism of active coke, considered as governing the catalytic performance of carbon materials in ODH of alkanes.This work was supported by the Polish National Science Centre under the grant no. DEC-2011/01/N/ST5/05595. The research was carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (contract No. POIG.02.01.00-12-023/08). The research was carried out using the infrastructure of the AGH Centre of Energy, AGH University of Science and Technology

A two-step pH control method to remove divalent metals from near-neutral mining and metallurgical waste drainages by inducing the formation of layered double hydroxide

A neutral M2+-rich and M3+-poor (M = metal) metallurgical waste drainage was used to test a metal removal method based on the precipitation of layered double hydroxide (LDH). The LDH precipitation was induced by adding a salt of Al3+ (trivalent metal missing in the drainage) and maintaining or restoring the pH to a circum-neutral value. The precipitates were characterized by chemical analysis, XRD, ESEM, HRTEM and XAS. The main parameter controlling the removal of metals and the type of precipitate appeared to be the pH. As a function of pH variation during the experiments, analyses of precipitates and solutions showed either the formation of poor crystalline LDH combined with very high removal of Zn, Ni and Pb (92–100%), more variable removal of Mn (46–98%) and less Cd (33–40%), or the formation of more crystalline LDH combined with lower removal of Zn (62%), Mn (43%), Ni (88%), Pb (64%) and especially Cd (1%). The different metal removal efficiency in the two cases is only indirectly due to the different LDH crystallinity, and it is clearly affected by the following factors: 1) the two pH steps of the method; 2) the direction of pH variation within each step. In particular, the highest removal of metals is obtained when the first pH step goes towards acidic conditions, as a consequence of Al salt addition, and precipitation of a quasi-amorphous hydrated hydroxysulfate of Al (probably a precursor of felsӧbányaite Al4(SO4)(OH)10 · 4H2O) occurs. This first acidic pH step removes little or no metals (just 0–3%) but it is essential so that the second pH step towards slightly alkaline conditions, as a consequence of NaOH addition, can be highly efficient in removing divalent metals as the quasi-amorphous hydrated hydroxysulfate of Al gradually turns into an LDH incorporating Zn, Mg and other metals. On the contrary, when both pH steps remain in the neutral-alkaline range, only LDH precipitation occurs and a lower metal removal is observed. These results encourage further investigations on the removal of metals by inducing LDH precipitation as a simple and effective method for the treatment of circum-neutral polluted drainages

Catalytic transfer hydrogenation of furfural to furfuryl alcohol over calcined MgFe hydrotalcites

Catalytic transfer hydrogenation is an alternative catalytic approach for the reduction of carbonyl groups, instead of the use of dihydrogen gas. In this sense, a series of catalysts has been prepared by thermal treatment of layered double hydroxides, hydrotalcite type, of Mg(II) and Fe(III), with different Mg/Fe molar ratios. The resulting mixture of metal oxides was characterized by X-ray diffraction, TEM, N2 adsorption-desorption, CO2-TPD, NH3-TPD and XPS, and then catalysts were tested in the Meenwein-Ponndorf-Verley (MPV) reduction of furfural to obtain furfuryl alcohol. The catalytic results show that the catalysts with a Mg/Fe molar ratio of 3 allows reaching the highest furfural conversion at a lower reaction time, with a FOL yield close to 90% after 6 h of reaction at 443 K. The detailed analysis of these catalysts also revealed that the basicity has a more predominant role in the MPV reaction than acid sites.Spanish Ministry of Innovation, Science and Universities (Project RTI2018-094918-B-C44) and FEDER (European Union) funds. J.A.C. and C.G.S. thank University of Malaga for contracts of PhD incorporation. R.M.T. thanks to the Spanish Ministry of Economy and Competitiveness (IEDI-2016-00743) for the financial support within the I3 program

Phase behavior of iron oxide doping with ethylbenzene dehydrogenation catalyst promoters

Potassium-promoted iron oxide is the primary catalyst for dehydrogenating ethylbenzene to styrene. Due to an increasing demand for saving energy, there is a strong incentive to operate the reaction at reduced steam/ethylbenzene molar ratio, since a large amount of steam is used in the process. However, the catalyst experiences short-term deactivation under low S/EB conditions. Active site blocking by surface carbon and iron oxide reduction by either surface carbon or H2 are two possible deactivation mechanisms. However, the relative importance of these two mechanisms is not understood. It is very important to understand which deactivation mechanism dominates as different mechanism will lead to different development approaches. In this study, phase transitions of iron oxide based catalyst samples were investigated with TGA and XRD to understand the intrinsic deactivation mechanism. The effects of various promoters on iron oxide activity and stability were also studied. Hydrogen and carbon dioxide were utilized as the gas environment individually to avoid convolution of effects. Ethylbenzene was then applied to characterize the combined effects of hydrogen, carbon dioxide, and surface coke. Potassium efficiently increases the activity of iron oxide and its effect on phase stability was examined. The active potassium ferrite phase and potassium polyferrite, which has been considered a storage phase of potassium and iron (III), can be converted to each other when exposed to carbon dioxide or hydrogen. It was also found that the deposited surface carbon was a stronger reductant than hydrogen. Other minor promoters are also used in dehydrogenation catalysts to enhance stability, enhance activity, or increase the styrene selectivity. Therefore, their effects on the catalyst were also examined in this study. Chromium, calcium, and cerium were found to have a positive effect on iron oxide stability, while vanadium and molybdenum had negative impacts on iron oxide stability. Activity enhancement could be achieved by doping with chromium, calcium, molybdenum, and cerium. Vanadium greatly reduced the activity of catalyst, since it inhibited formation of the active phase

Continuous-Flow O-Alkylation of Biobased Derivatives with Dialkyl Carbonates in the Presence of Magnesium-Aluminium Hydrotalcites as Catalyst Precursors

The base-catalysed reactions of OH-bearing biobased derivatives (BBDs) including glycerol formal, solketal, glycerol carbonate, furfuryl alcohol and tetrahydrofurfuryl alcohol with nontoxic dialkyl carbonates (dimethyl and diethyl carbonate) were explored under continuous-flow (CF) conditions in the presence of three Na-exchanged Y- and X-faujasites (FAUs) and four Mg\u2013Al hydrotalcites (HTs). Compared to previous etherification protocols mediated by dialkyl carbonates, the reported procedure offers substantial improvements not only in terms of (chemo)selectivity but also for the recyclability of the catalysts, workup, ease of product purification and, importantly, process intensification. Characterisation studies proved that both HT30 and KW2000 hydrotalcites acted as catalyst precursors: during the thermal activation pre-treatments, the typical lamellar structure of the hydrotalcite was broken down gradually into a MgO-like phase (periclase) or rather a magnesia\u2013alumina solid solution, which was the genuine catalytic phase