Dariusz Łomot

Sonophotodeposition of bimetallic photocatalysts Pd-Au/TiO2 : application to selective oxidation of methanol to methyl formate.

The aim of this work is to develop bimetallic Pd-Au/TiO2 P90 systems, which are highly active and selective for the photocatalytic oxidation of methanol to form methyl formate. Modification of commercial TiO2 P90 with Pd-Au nanoparticles was successfully achieved for the first time by means of a sonophotodeposition (SPD) method. The prepared materials were characterized by TEM, UV/Vis spectroscopy, X-ray photoelectron spectroscopy, and powder XRD. The Pd-Au bimetallic nanoparticles supported on titania exhibited remarkably enhanced catalytic activity in selective methanol oxidation to form methyl formate due to the synergism of Au and Pd particles, as well as the strong interaction between TiO2 and Pd-Au. SPD is a green methodology that can be used to prepare well-defined bimetallic surfaces on semiconductor supports with great promise for catalytic applications, in which selectivity can be tuned through adjustment of the surface composition.

Transformation of Pd/SiO2 Catalysts During High Temperature Reduction

During reduction in dihydrogen at 873 K, a silica-supported palladium catalyst is initially converted to Pd4Si which further reacts with silicon-containing species to a Pd3Si phase. Such a stepwise phase change suggests that the mechanism of Pd silicide formation involves incorporation of silicon into a palladium phase, not vice versa, as was suggested in our previous work. This transformation has a great effect on catalytic properties of Pd–silica-containing systems in 2,2-dimethylpropane hydroconversion.

A novel biomass-based support (Starbon) for TiO2 hybrid photocatalysts: a versatile green tool for water purification

The average size of the TiO2 nanoparticles was controlled at around 30 nm on Starbon 800 without using any surfactant, which is attributed to the hydrolysis and condensation (it is also proposed to be a plausible condensation with the carboxylate groups on the carbon surface) of the dissolved titanium(IV) isopropoxide into TiO2 by ultrasonic waves. As the Starbon in the composites has very good contact with the TiO2 nanoparticles (there is no Ti leaching after 240 min of photocatalysis, XRF analysis) it enhances the photo-electron conversion (better than Norit and graphene oxide carbons) of TiO2 by reducing the recombination of photo-generated electron–hole pairs. We have prepared an excellent new hybrid photocatalyst for aqueous phase phenol total mineralization.

Catalytic conversion of C6-alkanes over Pd/Al2O3 catalysts: The effect of support acidity

A comparable study of catalytic conversion of two C6-alkanes (n-hexane and 2,2-dimethybutane) has shown several analogies in the catalytic behavior of a series of differently loaded, chlorine-free Pd/Al 2O3 catalysts. Different sample pretreatments have been used to modify the catalytic behavior. The catalytic performance of lowly reduced (at 573 K) samples of Pd/Al2O3 catalysts is similar to that exhibited by unsupported or silica-supported palladium, i.e. the predominance of metal-catalyzed reactions is observed with high hydrogenolysis selectivity and a bond-shift mode of isomerization. Highly reduced (at 873 K) samples experience a serious increase in overall activity, and simultaneously, big enhancement of isomerization selectivity (at ≤563 K), in agreement with previous reports [1–3]. At the same time, the activity is strongly correlated with the amount of activated alumina in the catalyst and only insignificantly dependent on Pd content in the catalyst. TPD of ammonia has been employed to confirm expected changes in the acidity generated by various catalyst pretreatments. It is considered that Lewis acidity of alumina, increased upon high temperature reduction (HTR), is a source of enhanced isomerization activity exhibited by Pd/Al2O3 catalysts. However, a palladium-free alumina cannot serve as efficient catalyst in alkane hydroconversion. Metallic function is needed to provide active hydrogen for a hydrogenative desorption of rearranged hydrocarbon species from acid sites of -Al2O3.

The effect of Pd/Al2O3 pretreatment on catalytic activity in cyclopentane/deuterium exchange

Big variations in overall activity and product selectivity in the cyclopentane/deuterium exchange reaction were found in effect of various pretreatments of two chlorine‐free Pd/γ‐Al2O3 catalysts. The most important changes are observed when severely prereduced (at 600 °C) Pd/Al2O3 catalysts have been reoxidised and mildly rereduced: the multiple type of exchange, typical of mildly pretreated Pd catalysts, is replaced by a stepwise mode, and a big increase in catalytic activity occurs. At this state, the Pd/γ‐Al2O3 catalysts retain some water (as surface hydroxyls) generated by reoxidation and mild reduction. Deuterium spillover from Pd onto alumina and changes in acidity of alumina are invoked to rationalize the kinetic results. Changes in the state of Pd after various pretreatments, as probed by temperature‐programmed hydride decomposition, can hardly be correlated with changes in the catalytic behaviour in the exchange reaction.

Evolution of Pd/SiO2 catalysts prepared from chlorine-free precursors

The effect of pretreatment conditions on the final metal dispersion and chemistry of precalcination of Pd/SiO 2 catalysts prepared from Pd(NH 3 ) 4 (NO 3 ) 2 and palladium acetylacetonate [Pd(acac) 2 ] have been studied. The fate of the Pd(NH 3 ) 4 2+ /SiO 2 precursor strongly depends on precalcination conditions. In helium, a vast majority of the ammine ligands desorb in a stepwise fashion, whereas considerable amounts of N 2 , N 2 O and NO are also liberated at various stages of precalcination in O 2 –He. The latter finding, not observed by others, is explicable by the known propensity of palladium to catalyse NH 3 oxidation. Pretreatment of the Pd(NH 3 ) 4 2+ /SiO 2 in He leads to well dispersed reduced Pd species, but an analogous pretreatment in O 2 –He results in the formation of an even more dispersed PdO species. In precalcination of the Pd(acac) 2 /SiO 2 precursor, an oxidizing atmosphere and temperatures 250 °C are essential for complete removal of carbonaceous species. After decomposition in He, the catalytic role of a carbonaceous material, retained by Pd/SiO 2 , depends on the temperature of the pretreatment. The low-temperature treatment (at 250 °C), followed by reduction in H 2 , supposedly leads to a loosely packed carbonaceous residue, leaving a considerable part of the palladium surface still capable of 2,2-dimethylpropane conversion. On the other hand, a high-temperature decomposition of the Pd(acac) 2 precursor (at 500 °C) in He greatly suppresses the activity. It is speculated that the decomposition in He at 500 °C leads to a carbide-like surface material, which is not eliminated by reduction in H 2 .

Quick low temperature coalescence of Pt nanocrystals on silica exposed to NO – the case of reconstruction driven growth?

We report an operando XRD/MS experiment on nanocrystalline Pt supported on silica, monitoring quick growth of Pt in an NO atmosphere. XRD data following NO flow show structural changes typical of surface reconstruction. Although a small pressure of NO lifts surface reconstruction of a clean surface, a higher pressure of NO causes the surface to reconstruct again. TEM photographs show formation of clusters of Pt nanoparticles, pointing to growth controlled by coalescence. As surface reconstruction is the phenomenon that we always see accompanying quick growth, we postulate a mechanism of self-lifting cyclic reconstruction that drives the transport of whole clusters and their fusion.

Development of photocatalyst coated fluoropolymer based microreactor using ultrasound for water remediation

Formation of thin layers of photocatalyst in photo-microreactor is a challenging work considering the properties of both catalyst and the microchannel material. The deposition of semiconductor materials on fluoropolymer based microcapillary requires the use of economical methods which are also less energy dependent. The current work introduces a new method for depositing nanoparticles of TiO2 on the inner walls of a hexafluoropropylene tetrafluoroethylene microtube under mild conditions using ultrasound technique. During the ultrasonication process, changes in the polymer surface were observed and characterized using Attenuated Total Reflectance spectroscopy, Scanning Electron Microscopy and Confocal Microscopy. The rough patches form sites for catalyst deposition resulting in the formation of thin layer of TiO2 nanoparticles in the inner walls of the microtube. The photocatalytic activity of the TiO2 coated fluoropolymer based microcapillary was evaluated for removal of phenol present in water.

Catalytic activity of Pd-Ni in the oxidation of hydrogen for the safety of nuclear power plant

Abstract Pd-Ni/Al2O3 systems were investigated in the reaction of hydrogen oxidation in terms of their possible application as catalysts used in passive autocatalytic recombiners (PARs) used in nuclear power plants. Testing experiments were carried out in a flowing system at different temperatures and humidity of the reaction mixture. The bimetallic catalysts exhibited higher response to the increase of temperature and higher resistance to inhibit water than the monometallic palladium catalyst. They showed excellent stability during a few tens of hours, similarly, like their monometallic counterpart. Our bimetallic catalysts of hydrogen oxidation can be used as cheaper alternatives to catalysts based on the precious metals in the hydrogen oxidation without loss of their activity over time.