Must the best laboratory prepared catalyst also be the best in an operational application?

Three cobalt mixed oxide deN(2)O catalysts, with optimal content of alkali metals (K, Cs), were prepared on a large scale, shaped into tablets, and tested in a pilot plant reactor connected to the bypassed tail gas from the nitric production plant, downstream from the selective catalytic reduction of NOx by ammonia (SCR NOx/NH3) catalyst. High efficiency in N2O removal (N2O conversion of 75-90% at 450 degrees C, VHSV = 11,000 m(3) m(bed)(-3) h(-1)) was achieved. However, a different activity order of the commercially prepared catalyst tablets compared to the laboratory prepared catalyst grains was observed. Catalytic experiments in the kinetic regime using laboratory and commercial prepared catalysts and characterization methods (XRD, TPR-H-2, physisorption, and chemical analysis) were utilized to explain this phenomenon. Experimentally determined internal effectiveness factors and their general dependency on kinetic constants were evaluated to discuss the relationship between the catalyst activity in the kinetic regime and the internal diffusion limitation in catalyst tablets as well as their morphology. The theoretical N2O conversion as a function of the intrinsic kinetic constants and diffusion rate, expressed as effective diffusion coefficients, was evaluated to estimate the final catalyst performance on a large scale and to answer the question of the above article title.Web of Science92art. no. 16

Co-Mn-Al mixed oxides promoted by K for direct NO decomposition: Effect of preparation parameters

Fundamental research on direct NO decomposition is still needed for the design of a sufficiently active, stable and selective catalyst. Co-based mixed oxides promoted by alkali metals are promising catalysts for direct NO decomposition, but which parameters play the key role in NO decomposition over mixed oxide catalysts? How do applied preparation conditions affect the obtained catalyst's properties? Co4MnAlOx mixed oxides promoted by potassium calcined at various conditions were tested for direct NO decomposition with the aim to determine their activity, stability and selectivity. The catalysts were prepared by co-precipitation of the corresponding nitrates and subsequently promoted by KNO3. The catalysts were characterized by atomic absorption spectrometry (AAS)/inductive coupled plasma (ICP), X-ray photoelectron spectrometry (XPS), XRD, N-2 physisorption, temperature programmed desorption of CO2 (TPD-CO2), temperature programmed reduction by hydrogen (TPR-H-2), species-resolved thermal alkali desorption (SR-TAD), work function measurement and STEM. The preparation procedure affects physico-chemical properties of the catalysts, especially those that are associated with the potassium promoter presence. The addition of K is essential for catalytic activity, as it substantially affects the catalyst reducibility and basicity-key properties of a deNO catalyst. However, SR-TAD revealed that potassium migration, redistribution and volatilization are strongly dependent on the catalyst calcination temperature-higher calcination temperature leads to potassium stabilization. It also caused the formation of new phases and thus affected the main properties-S-BET, crystallinity and residual potassium amount.Web of Science97art. no. 59

K-modified Co-Mn-Al mixed oxide-effect of calcination temperature on N2O conversion in the presence of H2O and NOx

The effect of calcination temperature (500-700 degrees C) on physico-chemical properties and catalytic activity of 2 wt. % K/Co-Mn-Al mixed oxide for N2O decomposition was investigated. Catalysts were characterized by inductively coupled plasma spectroscopy (ICP), X-ray powder diffraction (XRD), temperature-programmed reduction by hydrogen (TPR-H-2), temperature-programmed desorption of CO2 (TPD-CO2), temperature-programmed desorption of NO (TPD-NO), X-ray photoelectron spectrometry (XPS) and N-2 physisorption. It was found that the increase in calcination temperature caused gradual crystallization of Co-Mn-Al mixed oxide, which manifested itself in the decrease in Co2+/Co3+ and Mn3+/Mn4+ surface molar ratio, the increase in mean crystallite size leading to lowering of specific surface area and poorer reducibility. Higher surface K content normalized per unit surface led to the increase in surface basicity and adsorbed NO per unit surface. The effect of calcination temperature on catalytic activity was significant mainly in the presence of NOx, as the optimal calcination temperature of 500 degrees C is necessary to ensure sufficient low surface basicity, leading to the highest catalytic activity. Observed NO inhibition was caused by the formation of surface mononitrosyl species bonded to tetrahedral metal sites or nitrite species, which are stable at reaction temperatures up to 450 degrees C and block active sites for N2O decomposition.Web of Science1010art. no. 113

Catalytic oxidation of ammonia over cerium-modified copper aluminium zinc mixed oxides

Copper-containing mixed metal oxides are one of the most promising catalysts of selective catalytic oxidation of ammonia. These materials are characterized by high catalytic efficiency; however, process selectivity to dinitrogen is still an open challenge. The set of Cu-Zn-Al-O and Ce/Cu-Zn-Al-O mixed metal oxides were tested as catalysts of selective catalytic oxidation of ammonia. At the low-temperature range, from 250 & DEG;C up to 350 & DEG;C, materials show high catalytic activity and relatively high selectivity to dinitrogen. Samples with the highest Cu loading 12 and 15 mol.% of total cation content were found to be the most active materials. Additional sample modification by wet impregnation of cerium (8 wt.%) improves catalytic efficiency, especially N-2 selectivity. The comparison of catalytic tests with results of physicochemical characterization allows connecting the catalysts efficiency with the form and distribution of CuO on the samples' surface. The bulk-like well-developed phases were associated with sample activity, while the dispersed CuO phases with dinitrogen selectivity. Material characterization included phase composition analysis (X-ray powder diffraction, UV-Vis diffuse reflectance spectroscopy), determination of textural properties (low-temperature N-2 sorption, scanning electron microscopy) and sample reducibility analysis (H-2 temperature-programmed reduction).Web of Science1421art. no. 658

The Physiology and Proteomics of Drought Tolerance in Maize: Early Stomatal Closure as a Cause of Lower Tolerance to Short-Term Dehydration?

Understanding the response of a crop to drought is the first step in the breeding of tolerant genotypes. In our study, two maize (Zea mays L.) genotypes with contrasting sensitivity to dehydration were subjected to moderate drought conditions. The subsequent analysis of their physiological parameters revealed a decreased stomatal conductance accompanied by a slighter decrease in the relative water content in the sensitive genotype. In contrast, the tolerant genotype maintained open stomata and active photosynthesis, even under dehydration conditions. Drought-induced changes in the leaf proteome were analyzed by two independent approaches, 2D gel electrophoresis and iTRAQ analysis, which provided compatible but only partially overlapping results. Drought caused the up-regulation of protective and stress-related proteins (mainly chaperones and dehydrins) in both genotypes. The differences in the levels of various detoxification proteins corresponded well with the observed changes in the activities of antioxidant enzymes. The number and levels of up-regulated protective proteins were generally lower in the sensitive genotype, implying a reduced level of proteosynthesis, which was also indicated by specific changes in the components of the translation machinery. Based on these results, we propose that the hypersensitive early stomatal closure in the sensitive genotype leads to the inhibition of photosynthesis and, subsequently, to a less efficient synthesis of the protective/detoxification proteins that are associated with drought tolerance

Chemical recycling of waste polystyrene by thermo-catalytic pyrolysis: A description for different feedstocks, catalysts and operation modes

Chemical recycling by thermo-catalytic pyrolysis/degradation offers the possibility of converting waste plastics into their original monomers or other valuable chemicals which can be used as feedstocks in chemical and petrochemical industries. Plastic wastes of polystyrene (PS) based materials can be a good source of styrene as well as mono-aromatic (BTEX: benzene, toluene, ethylbenzene, xylenes) compounds. The selectivity of pyrolysis products can be tuned by choosing the right catalyst as well as appropriate operating conditions/operation modes. In this regard, the focus of the present work was to perform thermo-catalytic pyrolysis of different waste polystyrene (WPS) feedstocks over acid and base catalysts employed in ex-situ and in-situ modes. The main goal was to compare the compositions of pyrolysis products obtained by changing feedstocks, catalysts and operation modes. A further goal was to discuss the suitability of the catalysts employed for the enhanced recovery of desired products from WPS pyrolysis. It was demonstrated that expanded polystyrene gives very similar product distribution as compared to virgin PS, both giving high styrene content. Likewise, hard PS-based random packing materials produce similar results as compared to high impact polystyrene (HIPS). Moreover, it was shown that solid base catalysts influence the composition of the pyrolysis products only slightly as compared to thermolysis. Solid acid catalyst however, showed significant impact on the composition of the pyrolysis products as compared to non-catalytic pyrolysis. These results may provide new insights for the chemical recycling of plastic wastes.Web of Science201art. no. 10998

Modification of Ni/ZrO2 catalyst by selected rare earth metals as a promising way for increase in the efficiency of thermocatalytic conversion of lignocellulosic biomass to hydrogen-rich gas

The main goal of this work was the evaluation of the effect of modification of zirconia by selected rare earth metals (praseodymium, yttrium and gadolinium) on the activity of nickel catalyst in the high temperature conversion of lignocellulosic biomass to hydrogen-rich gas. An influence of type of dopant, its content and introduction method was studied. The obtained results revealed that the modification of catalysts allowed for noticeable increase the efficiency of hydrogen-rich gas production in the high temperature conversion of lignocellulosic feedstock. The highest activity among studied catalysts was observed for nickel supported on zirconium oxide modified by praseodumium via sol-gel method. The performed experiments (XRD, XPS, TEM, TPR, TPD-NH3, TG-DTA-MS and BET) indicated that an increase in the activity of investigated catalysts can be not only related with larger surface area, pore volume and higher acidity, but also size and location of active phase crystallites, susceptibility of nickel oxide to the reduction and contribution of Pr3+ ions in zirconia lattice.Web of Science276art. no. 11811

Reaction mechanism of NO direct decomposition over K-promoted Co-Mn-Al mixed oxides – DRIFTS, TPD and transient state studies

The reaction mechanism of direct NO decomposition over Co4MnAlOx mixed oxides prepared by co-precipitation method and promoted by 0-3.1 wt.% of potassium was studied. Temperature programmed desorption of NO and in-situ diffuse reflectance infrared Fourier transform spectroscopy confirmed the presence of several nitrogen species (adsorbed NO, NO-,NO2-, and NO3-) present on the catalyst surface and revealed that O2 desorption occurs at the high temperature region together with the NO desorption as the product of NO2and/or NO3- decomposition. This region corresponds with the temperature of launching NO conversion curve, which together with the results from the transient state experiments proved that O2 desorption is the slowest step while the reaction steps including NOx-formation and those leading to N2 release are fast. The Langmuir-Hinshelwood mechanism was proposed as a plausible way of direct NO decomposition over K/ Co4MnAlOx catalysts and NO2- and NO3- were determine as the main reaction intermediates.Web of Science12026625

Cobalt oxide catalysts on commercial supports for N2O decomposition

Co3O4 oxide catalysts prepared on different commercial supports, namely, TiO2, Al2O3, and Mg-Al mixed oxides with various Mg and Al concentrations, were characterized by atomic absorption spectrometry, Brunauer-Emmett-Teller method, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and H-2 temperature-programmed reduction, tested for N2O decomposition, and compared with bulk Co3O4. In spite of the fact that Co3O4/70Mg30Al also contained hardly reducible compounds, it possessed the highest catalytic activity, probably due to the presence of active sites with easier reducibility and better dispersion of the active phase on the support contributing to a higher number of active sites. The conversion over Co3O4-supported tablets is comparable with that of the same catalyst bed of bulk Co3O4 tableted catalyst.Web of Science40599098

Catalytic activity of rhodium grafted on ordered mesoporous silica materials modified with aluminum in N2ON_2O decomposition

Three different ordered mesoporous silica materials, such as MCM-41, Al-containing MCM-41 (with 1.6 wt% of Al incorporated into the silica framework) and SBA-15, were prepared. Furthermore, aluminum (1.8 wt%) was grafted on the silica surface by the molecular designed dispersion method (MDD). In a next step, rhodium (1.4–2.9 wt%), as an active metal for the catalytic reaction of N2O decomposition, was introduced by the MDD technique. The following order of the catalytic activity was found under an inert atmosphere: Al(incorporated)-MCM-41 + Rh > MCM-41 + Al(grafted) + Rh > SBA-15 + Rh ≈ MCM-41 + Rh. The influence of textural properties, total acidity and rhodium dispersion on the activity of catalysts was studied