Atomic Layer Deposition Catalysts Research Articles

Bifunctional Mn‐Fe Oxide Catalysts for Zn‐Air Battery Air Electrodes Fabricated Through Atomic Layer Deposition

Zinc‐air batteries (ZABs) are one of many energy storage technologies that can help integrate renewable energy into the power grid. A key developmental goal for ZABs is replacing the precious metal catalysts at the air electrode with more abundant and inexpensive materials. In this work, a MnFexOy bifunctional catalyst is directly deposited on a ZAB air electrode using atomic layer deposition (ALD). With ALD, the atomic composition of the air electrode coating can be tuned based on catalytic activity. Characterization through electron microscopy, photoelectron spectroscopy and diffraction techniques indicate that the novel ALD film deposits as a nanocrystalline (Mn,Fe)3O4 cubic spinel. The mixed oxide catalyst outperforms its individual binary MnOx or FeOx constituents, operating at 50.7% bifunctional efficiency at 20 mA cm‐2. Moreover, the long term stability of the ALD catalyst is showcased by 600 h (1565 cycles) of ZAB cycling at 10 mA cm‐2. The efficiency retention of the bifunctional transition metal oxide catalyst is superior to a precious metal benchmark of Pt‐Ru‐C, with 84.7% efficiency retention after more than 1500 cycles versus only 66.2% retention for the precious metal catalyst. The ALD technique enables deep penetration of catalyst material into the air electrode structure, improving the cycling behaviour.

Pt/C catalysts synthesized in a commercial particle atomic layer deposition system enabling improved durability in fuel cells.

Particle atomic layer deposition (ALD) is an emerging method for engineering 3D materials, such as powders, for energy applications. In our study, we employ a commercially available and scalable particle ALD system to synthesize Pt/C electrocatalysts for fuel cells. Our method yields Pt/C catalysts characterized by highly dispersed platinum nanoparticles with a narrow particle size distribution of 2.2 ± 0.5 nm for 30 wt% Pt and 2.6 ± 0.6 nm for 40 wt% Pt, as verified through transmission electron microscopy and X-ray diffraction analysis. The performance of the ALD-synthesized catalysts is benchmarked against a state-of-the-art catalyst (TEC10V50E), with both catalysts exhibiting similar beginning-of-test performance (1.6 A cm-2 at 0.65 V) under application-relevant operation conditions (80 °C, 50% relative humidity). After 30 000 voltage cycles, conducted in accordance with the U.S. Department of Energy's accelerated catalyst degradation test, the ALD catalysts demonstrate up to 64% greater electrochemical active surface areas and superior retention of cell performance, with a 34% higher current density at 0.65 V, compared to the reference. Given the scalability of the commercial particle ALD system, these promising results encourage the use of particle ALD as a novel synthesis approach for fuel cell catalyst materials in the industry.

Atomic Layer Deposition of the Geometry Separated Lewis and Brønsted Acid Sites for Cascade Glucose Conversion.

Solid acid catalysts with bi-acidity are promising as workhouse catalysts in biorefining to produce high-quality chemicals and fuels. Herein, we report a new strategy to develop bi-acidic cascade catalysts by separating both acid sites in geometry via the atomic layer deposition (ALD) of Lewis acidic alumina on Brønsted acidic supports. Visualized by transmission electron microscopy and electron energy loss spectroscopy mapping, the ALD-deposited alumina forms a conformal alumina domain with a thickness of around 3 nm on the outermost surface of mesoporous silica-alumina. Solid state nuclear magnetic resonance investigation shows that the dominant Lewis acid sites distribute on the outermost surface, whereas intrinsic Brønsted acid sites locate inside the nanopores within the silica-rich substrate. In comparison to other bi-acidic solid catalyst counterparts, the special geometric distance of Lewis and Brønsted acid sites minimized the synergetic effect, leading to a cascade reaction environment. For cascade glucose conversion, the designed ALD catalyst showed a highly enhanced catalytic performance.

Tubular PEM electrolysis cells with a 3D-printed oxygen electrode and ALD catalyst coating

Polymer electrolyte membrane electrolysis (PEMEL) is a technology with a major role in linking the hydrogen production to renewable energy resources with a volatile behaviour such as wind and solar. High amounts of precious metals and a labour intensive production also make it a cost intensive technology. A tubular cell design has the potential to reduce production costs by co-extrusion of cells which feature a reduced sealing length. For the inner half cell, additive manufacturing (AM) of titanium offers a high degree of freedom for the electrode design to reach a high electric conductivity and active surface area. In combination with atomic layer deposition (ALD) of iridium catalyst a porous transport electrode (PTE) can be fabricated. Using planar test cell results and model based PTE design, this study demonstrates the feasibility of a tubular PEMEL cell consisting of an additively manufactured, iridium coated anode PTE in the inner half cell, an extruded membrane and a platinum coated graphite felt cathode PTE in the outer half cell. The outer titanium current collector can be replaced by an extruded graphite polymer compound current collector to reduce the amount of titanium without performance losses. The cell is operated at 60 °C in 1 mol L−1 sulphuric acid and experimentally characterized by polarization curves and electrochemical impedance spectroscopy (EIS). At 2.0 V cell potential a current density of ≈450mAcm−2 was reached corresponding to an iridium mass specific current density >1500Ag−1 which is significant larger than literature values.

Highly dispersed atomic layer deposited CrOx on SiO2 catalyst with enhanced yield of propylene for CO2 –mediated oxidative dehydrogenation of propane

The increasing worldwide demand for propylene and the necessity of CO2 mitigation attracted the attention of scientists to focus on CO2-oxidative dehydrogenation of propane (CO2-ODHP). In this regard, CrOx/SiO2 catalyst is an important and conventional option. Herein, we studied the atomic layer deposition (ALD) of CrOx on silica to increase the propylene production by increasing the dispersion of the catalyst. For ALD synthesis of CrOx/SiO2 catalyst, Cr(acac)3 and synthetic air were used as metal precursor and oxidant. The catalysts were examined in the CO2-ODHP reaction and their characteristics were compared to their impregnation counterparts using UV–Vis DRS, Raman, XANES, HRTEM and STEM-EDS mapping, H2-TPR, NH3-TPD and TPO. The ALD catalysts have shown up to 2 times higher acidity and enhanced reducibility compared to the impregnation catalysts. The presence of mainly Cr(VI) with a pre-edge peak at 5.994 keV in both series of catalysts was confirmed by XANES. UV–Vis DRS and Raman spectroscopy revealed the higher contents of active polymeric Cr(VI) species in the ALD ones. The dark field HRTEM and STEM-EDS mapping represented higher dispersion of chromium oxide particles in ALD catalysts. In CO2-ODHP, the ALD catalysts showed up to 18 and 15% promotion in propane conversion and propylene yield.

Effect of Co-fed Water on a Co–Pt–Si/γ-Al2O3 Fischer–Tropsch Catalyst Modified with an Atomic Layer Deposited or Molecular Layer Deposition Overcoating

Atomic layer deposition (ALD) and molecular layer deposition (MLD) methods were used to prepare overcoatings on a cobalt-based Fischer–Tropsch catalyst. A Co–Pt–Si/γ-Al2O3 catalyst (21.4 wt % Co, 0.2 wt % Pt, and 1.6 wt % Si) prepared by incipient wetness impregnation was ALD overcoated with 30–40 cycles of trimethylaluminum (TMA) and water, followed by temperature treatment (420 °C) in an inert nitrogen atmosphere. MLD-overcoated samples with corresponding film thicknesses were prepared by using TMA and ethylene glycol, followed by temperature treatment (400 °C) in an oxidative synthetic air atmosphere. The ALD catalyst (40 deposition cycles) had a positive activity effect upon moderate water addition (PH2O/PH2 = 0.42), and compared with a non-overcoated catalyst, it showed resistance to irreversible deactivation after co-fed water conditions. In addition, MLD overcoatings had a positive effect on the catalyst activity upon moderate water addition. However, compared with a non-overcoated catalyst, only the 10-cycle MLD-overcoated catalyst retained increased activity throughout high added water conditions (PH2O/PH2 = 0.71). All catalyst variations exhibited irreversible deactivation under high added water conditions.

Water management implications for ALD-modified polymer electrolyte membrane fuel cell catalysts

Device testing of polymer electrolyte membrane fuel cell catalysts is essential for electrocatalyst development, yet most reported catalysts fabricated with nanoceramic coatings via atomic layer deposition (ALD) have not been thoroughly examined in this fashion. Platinum nanoparticle catalysts supported on functionalized XC72 carbon black that had been modified with sub-monolayer WN films and subjected to various thermal treatments were incorporated into membrane electrode assemblies and tested for oxygen reduction reaction activity in a fuel cell. The mass activities of the catalysts calculated at low current densities had comparable trends to those previously recorded in aqueous half-cell testing; however, significant deviations in catalyst performance became apparent at high current densities in the mass transport region of the polarization curves. The poor performance of the ALD-modified catalysts was attributed to water flooding induced by the low hydrophobicity of these catalyst layers, as determined by contact angle measurements on the cathode surfaces. It was seen that hydrophobicity was increased by thermal treatment and removal of surface groups known to be prone to hydrogen bonding, thereby improving the catalyst performance in the mass transport region. A heat-treated WN-coated ALD catalyst was found to have superior performance to commercial Pt/C. The field of research on fuel cell catalyst design via ALD is rapidly expanding, and this work demonstrates the importance of understanding the impact of ALD-deposited nanostructures on materials properties beyond the pure electrocatalytic activity.

Titania-Supported Vanadium Oxide Synthesis by Atomic Layer Deposition and Its Application for Low-Temperature Oxidative Dehydrogenation of Propane

Vanadium oxide supported on TiO2(P25) catalysts were synthesized via atomic layer deposition (ALD) of vanadyl acetylacetonate (VO(acac)2). Comprehensive investigations were performed to evaluate the ALD temperature window and the saturation deposition period of VO(acac)2, which were found to be 140–210 °C and 120 min, respectively. The synthesized catalysts were compared to their corresponding impregnation ones for the oxidative dehydrogenation of propane reaction (ODH-P). The ODH-P results indicated the superior performance of the ALD catalysts for the low temperature ODH-P (< 350 °C) given its better dispersion of vanadium oxide(vanadia) in the ALD catalysts. Several characterization techniques including HR-TEM, FE-SEM, XRD, BET, XPS, O2-chemisorption, ICP-OES, and H2-TPR were utilized to evaluate the influence of the ALD and impregnation methods of synthesis on different features of the catalysts. It was observed that the ALD method could offer far better dispersion of the active phase on the support of the catalyst, which is beneficial for the catalytic performance. Variations of Hacac, acetone, and CO2 FTIR absorbance peaks’ areas versus the support temperature

Rational Design of Novel Catalysts with Atomic Layer Deposition for the Reduction of Carbon Dioxide

AbstractCarbon dioxide (CO2) is one of the end products of fuel combustion and the major component of the greenhouse gases. The reduction of atmospheric CO2 not only decreases environmental pollution but also produces value‐added chemicals, solving energy and environment issues simultaneously. One significant challenge is the low conversion efficiency of CO2 reduction due to the inertness of the CO2 molecule. The design of the catalyst nanomaterials with the high selectivity, stability, and the activation capabilities for the conversion of CO2 is needed. Atomic layer deposition (ALD), capable of constructing catalysts with atomic‐level precision in a highly controllable manner, is a promising technique to address the key problems in CO2 reduction. This review explores the application of ALD in CO2 reduction, emphasizing the designs of the efficient catalyst nanomaterials fabricated by the ALD technique and their applications in CO2 reduction and capture. The significance of the ALD catalysts with the fine structures is highlighted to obtain a better understanding of the catalytic performance–aimed benefits as well as an outlook on the ALD‐designed catalysts for the reduction of CO2.

Atomic layer deposited Palladium nanoparticle catalysts supported on Titanium dioxide modified MCM-41 for selective hydrogenation of acetylene

In the chemical industry palladium-based catalysts are commonly used to remove trace amounts of acetylene from ethylene feed. In this work atomic layer deposition (ALD) is utilized to synthesize uniformly dispersed Pd nanoparticles inside the meso-pores of a silica molecular sieve MCM-41. The space confinement effect from the internal channels of the molecular sieve leads to a very narrow size distribution (2–3 nm) of Pd nanoparticles and effectively prevents the particles from sintering during high temperature treatments. In selective hydrogenation of acetylene the ALD Pd nanoparticle catalysts exhibit excellent catalytic performances under ambient temperature and pressure. The excellent performance of the ALD catalyst is attributed to small Pd nanoparticles uniformly dispersed in the meso-pores of MCM-41 so that more Pd surface sites are available for the catalytic reaction. The strong metal support interaction between Pd and TiO2 can be induced by high temperature treatments, which suppresses the surface adsorption of both acetylene and ethylene, leading to decreased acetylene conversion and improved ethylene selectivity. The high temperature treatment also helps improve the stability of the catalysts.

Improved durability and activity of Pt/C catalysts through atomic layer deposition of tungsten nitride and subsequent thermal treatment

Atomic layer deposition (ALD) of tungsten nitride (WN) enhanced the durability and activity of a carbon-supported Pt nanoparticle oxygen reduction reaction (ORR) catalyst by adding protective WN nanostructures to the surface. A post-synthesis thermal treatment sequence of low-temperature oxidation followed by high-temperature reduction was carried out on the ALD-modified catalyst. The effects of the ALD process and thermal treatment on the structure and electrochemical properties of the catalyst were examined. Characterization through ICP-MS, STEM and EDS mapping, and X-ray diffraction showed that the ALD process deposited WN homogenously across the surface. Thermal treatment resulted in a reduced amount of nitride on the surface and produced separate Pt and W domains. The electrochemical performance of the catalysts is measured through rotating disk electrode voltammetry. The thermally-treated ALD catalyst was observed to have a high mass activity towards the ORR (465 mA/mg), surpassing benchmark Pt/C (277 mA/mg), and demonstrated superior retention of electrochemical properties after an accelerated durability test. Analysis of particle size distributions before and after durability testing also indicated that the mechanical stability of the Pt nanoparticles is enhanced in the thermally-treated ALD catalyst compared to the uncoated materials.

Atomic layer deposition of TiO2 for stabilization of Pt nanoparticle oxygen reduction reaction catalysts

Atomic layer deposition (ALD) was used to modify two different types of carbon black-based Pt oxygen reduction catalysts with protective TiO2 nanostructures to increase catalyst durability. Rates of ALD growth and the structure of deposited TiO2 were observed to be highly dependent on oxygen content of the catalyst substrate. Electrochemical durability was enhanced with the addition of TiO2 ALD nanostructures, with up to 70% retention in mass activity measured over accelerated durability testing. High-temperature treatment of the top-performing ALD catalyst, which was found to promote structural rearrangement of the TiO2 and Pt phases into hybrid nanoparticles, yielded a twofold increase in activity but was detrimental to durability.

Proton Exchange Membrane Fuel Cell Flooding Caused by Residual Functional Groups after Platinum Atomic Layer Deposition

Proton exchange membrane fuel cell (PEMFC) catalysts manufactured using atomic layer deposition (ALD) on unmodified and functionalized carbon were compared to a commercial catalyst in half- and whole-cell tests. Half-cell tests showed the ALD catalyst performed better or comparable to a commercial catalyst. Conversely, whole-cell tests revealed flooding in the ALD catalyst produced on functionalized carbon. Residual functional groups had reduced the hydrophobicity, and rendered this catalyst impractical for use in whole-cell PEMFC applications. However, the ALD catalyst produced on unmodified carbon performed better than the commercial catalyst, which illustrates the power of ALD on appropriate catalyst supports.

Atomic layer deposited Co/γ-Al2O3 catalyst with enhanced cobalt dispersion and Fischer–Tropsch synthesis activity and selectivity

Co/γ-Al2O3 catalysts were prepared by atomic layer deposition (ALD) of Co(acac)2 and impregnation of Co(NO3)2, characterized by HRTEM, XRD, XPS, TPR, H2-TPD, O2 titration, and Raman spectroscopy methods, and used for Fischer–Tropsch synthesis (FTS). The ALD temperature window for self-limited chemisorption of Co(acac)2, rather than its condensation at lower or decomposition at higher temperatures, is 175–205°C. The period for Co(acac)2 saturated chemisorption and its complete reaction with ozone are also determined. Smaller cubic Co3O4 nanoparticles are formed in the ALD method, while spherical ones are developed in the impregnation method. The ALD catalysts have up to 2.3 times higher dispersions at the lower number of ALD cycles. However, more cobalt aluminates are formed on the ALD catalysts. In FTS, the catalyst with 6 ALD cycles shows 38% higher conversion, 30% higher C5+ selectivity, 28% less methane selectivity, and stabilizes at earlier time on stream, as compared to the impregnation catalyst with the same loading.

Electrochemical hydrogen pumping using a platinum catalyst made in a fluidized bed via atomic layer deposition

Platinum nanoparticle catalysts for electrochemical hydrogen pumping were synthesized on a functionalized powder carbon substrate (XC72R) using atomic layer deposition (ALD) in a fluidized bed reactor (FBR). Trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPtMe3) was used as the reagent for platinum delivery. Following deposition, MeCpPtMe3 ligands were combusted or hydrogenated to yield platinum on the XC72R surface. Reactions throughout the ALD cycle were monitored using mass spectrometry and IR spectroscopy to clarify the deposition chemistry. The resultant platinum catalysts were compared to commercial products in hydrogen pumping tests. Hydrogenation made finer, more dispersed, platinum nanoparticles that performed similarly to their commercial equivalent when pumping hydrogen. Conversely, oxygenation made a coarser catalyst that underperformed its commercial equivalent. Thus, altering chemistries shows potential for improving ALD catalyst performance.

Enhanced dry reforming of methane on Ni and Ni-Pt catalysts synthesized by atomic layer deposition

Atomic layer deposition (ALD) was used to deposit Ni and Pt on alumina supports to form monometallic and bimetallic catalysts with initial particle sizes of 1–2.4nm. The ALD catalysts were more active (per mass of metal) than catalysts prepared by incipient wetness (IW) for dry reforming of methane (DRM), and they did not form carbon whiskers during reaction due to their sufficiently small size. Catalysts modified by Pt ALD had higher rates of reaction per mass of metal and inhibited coking, whereas NiPt catalysts synthesized by IW still formed carbon whiskers. Temperature-programmed reduction of Ni catalysts modified by Pt ALD indicated the presence of bimetallic interaction. Density functional theory calculations suggested that under reaction conditions, the NiPt surfaces form Ni-terminated surfaces that are associated with higher DRM rates (due to their C and O adsorption energies, as well as the CO formation and CH4 dissociation energies).

Atomic Layer Deposited Platinum Electrocatalysts on Chemically Functionalized Graphene

Electrocatalysts play important roles in the performance of electrochemical energy conversion devices such as fuel cells and photoelectrochemical cells. Graphene is a promising candidate for the backbone structure for electrocatalysts due to its large surface area (theoretical value of 2630 m2/g) and good electrical conductivity. Catalyst particles, e.g., Pt nanoparticles, can be integrated with graphene via wet-process route, physical vapor deposition, or chemical vapor deposition. Catalyst-graphene composite materials synthesized via these routes, however, often suffer from low chemical/mechanical stabilities, low particle density, or non-uniform coverage [1,2].Atomic layer deposition (ALD), which is a modified chemical vapor deposition (CVD) method, is capable of decorating dense nanoparticles chemically bonded to 3-dimensional substrates in a uniform manner. In ALD, the substrate is exposed to the alternate pulses of precursor molecules, and coated with nanoparticles or conformal thin film depending on the cycle numbers. Nevertheless, the integration of graphene with ALD catalyst particles, e.g. Pt, has been challenging because the basal plane of the pristine graphene is chemically inert due to strongly sp2-bonded carbon atoms where the nucleation cannot readily occur [3].To this end, we present a chemical functionalization method of graphenes for the subsequent ALD platinum nucleation. We show that the low-power hydrogen plasma treatment hydrogenates the basal plane of graphene and significantly increases the chemical reactivity of the basal plane, facilitating the nucleation of the Pt nanoparticles by ALD. We systematically study the dependence of the particle density and the areal coverage on the graphene thickness and on the hydrogenation duration. While the areal coverage of Pt nanoparticles on the basal plane of the pristine graphene is negligible after 100 cycles of ALD Pt (<5 %), that of the few layer graphene hydrogenated for 2 mins hugely increases to > 80 %.We also investigate the individual particle shape, facets, and the interface between the particle and the graphene in atomic scale using probe-corrected scanning TEM (TEAM1). We show that the ALD Pt particle has epitaxially grown on the graphene with a large density of high-index facets, which makes it a promising candidate for mechanically and chemically stable electrocatalyst with high catalytic activity. Acknowledgment We thank Precourt Institute of Energy at Stanford university for financial support.

Scalable synthesis of palladium nanoparticle catalysts by atomic layer deposition

Atomic layer deposition (ALD) was used to produce Pd/Al2O3 catalysts using sequential exposures of Pd(II) hexafluoroacetylacetonate and formalin at 200 °C in a fluidized bed reactor. The ALD-prepared Pd/alumina catalysts were characterized by various methods including hydrogen chemisorption, XPS, and TEM, and compared with a commercially available 1 wt% Pd/alumina catalyst, which was also characterized. The content of Pd on alumina support and the size of Pd nanoparticles can be controlled by the number of ALD-coating cycles and the dose time of the Pd precursor. One layer of organic component from the Pd precursor remained on the Pd particle surface. The ALD 0.9 wt% Pd/alumina had greater active metal surface area and percent metal dispersion than the commercial 1 wt% Pd/alumina catalyst. The ALD and commercial catalysts were subjected to catalytic testing to determine their relative activities for glucose oxidation to gluconic acid in aqueous solution. The ALD 0.9 wt% Pd/alumina catalyst had comparable activity as compared to the commercial 1 wt% Pd catalyst. No noticeable amount of Pd leaching was observed for the ALD-prepared catalysts during the vigorously stirred reaction.

Surface characteristics and activity in selective oxidation of o-xylene of supported V 2O 5 catalysts prepared by standard impregnation and atomic layer deposition

Alumina-, silica-, and titania-supported vanadium oxide systems with V 2O 5 loadings ranging from 3 to 12 wt.%, corresponding to 0.02–0.09 V/(Al,Si,Ti) atomic ratios, were prepared by atomic layer deposition (ALD) and compared with the corresponding impregnated catalysts. The surface acidic properties of the supports and catalysts were investigated using ammonia adsorption microcalorimetry to determine the number and strength of the surface acid sites. Deposition of V 2O 5 on alumina and titania supports gave rise to catalysts with lower amounts of acid sites than the respective supports, while for the samples prepared on silica, an increase of the number of acid sites was observed after V 2O 5 deposition. As a common trend, the surface acid strength was greater for the ALD catalysts than for the impregnated ones, suggesting a stronger interaction of the VO species with the support centers, which act as electron attractor centers creating Lewis-like vanadium species. Redox cycles were performed, involving temperature programmed reduction (TPR) analyses separated by an oxidation treatment (TPO). The results evidenced the good reversibility of the redox behavior of the vanadium centers in every case, while significant differences were observed when comparing the temperatures of reduction ( T max). Lower T max values were observed for the better dispersed vanadia catalysts. After reduction, the V centers had a final formal average oxidation state corresponding to +3 or less (+2.5 to +2). The reactivity of the vanadia systems was examined by measuring their performance for the oxidation of o-xylene to phthalic anhydride. Activity tests indicated the superior selectivity of the V 2O 5 systems based on the more acidic supports (Al 2O 3 and TiO 2). The nature of the support governed the activity, and the more concentrated catalysts gave rise to improved selectivity to phthalic anhydride.

Gas-phase synthesis, structure and surface acid–base properties of highly dispersed vanadia/titania/silica catalysts

The atomic layer deposition (ALD) method based on surface-saturating gas-solid reactions was applied to grow vanadia species on highly dispersed titania/silica supports with from submono- to above monolayer levels of titania. The physicochemical properties of the V2O5/TiO2/SiO2 catalysts were examined with N2 adsorption, XRD, XPS and Raman spectroscopy techniques. The catalysts were compared to the corresponding titania supported catalysts, and besides a series of liquid-phase impregnated samples were characterized for comparison. In the ALD catalysts, isolated and highly dispersed tetracoordinated VOx species were formed on titania/silica supports with only small impact on the surface area and porosity of the support. Vanadia was homogeneously associated with both the surface titania species and the uncovered silica support. However, in the impregnated catalysts, crystalline vanadia at low titania coverage and TiOx agglomeration at high titania level decreased the surface area. Vanadia had also a preferential interaction with the titania phase. Moreover, the better dispersion of the active species in the ALD catalysts was confirmed by XPS of NH3 adsorption and microcalorimetry of NH3 and SO2 adsorption. The number and strength of acid–base sites on the surface of the catalysts were directly related to the V–O–Ti and V–O–Si concentrations as well as to the titania and vanadia dispersion in the samples, in favor of the ALD catalysts.