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Applied Catalysis A, General (v.345, #2)
Methane steam reforming for hydrogen production using low water-ratios without carbon formation over ceria coated Ni catalysts by Jiahui Xu; Connie M.Y. Yeung; Jun Ni; Frederic Meunier; Nadia Acerbi; Martin Fowles; Shik Chi Tsang (pp. 119-127).
There are many advantages for hydrogen production from catalytic methane steam reforming reaction using low water to methane ratios (<1). However, conventional Ni catalysts suffer from severe carbon deposition leading to a rapid deactivation. We show a stable and high level of hydrogen production with no carbon deposition over Ni commercial catalyst pre-coated with ceria using a sol–gel method.▪There are many advantages for hydrogen production from the catalytic methane steam reforming reaction (MSR) using low water to methane ratios. However, conventional Ni based catalysts suffer from severe carbon deposition under these conditions. A typical supported Ni catalyst at water to methane ratios <1 at 800°C shows rapid deactivation (within few hours). Incorporation of CeO2 is known to offer a kinetic resistance to carbon deposition for many hydrocarbon oxidation reactions because of its facilitated redox activity. As a result, a study of blending ceria into a supported Ni catalyst by a number of deposition methods has been carried out. Catalyst characterization including DRIFTS, XRD, TPR, TGA, TEM and EDX suggests the prime importance of an intimate contact between Ni and CeO2 in reducing the extent of carbon deposition during the reforming reaction, which critically depends on the preparation method in catalyst synthesis. As a result, a stable and high level of hydrogen production with no significant carbon deposition for over 110h is demonstrated over the same Ni commercial catalyst pre-coated with ceria using a sol–gel method, which offers the best interface for the reaction.
Keywords: Sol–gel method; Ceria; Ni catalyst; Methane steam reforming (MSR); Carbon deposition
Silica sulfuric acid as an efficient catalyst for the preparation of 2 H-indazolo[2,1- b]phthalazine-triones by Hamid Reza Shaterian; Majid Ghashang; Mostafa Feyzi (pp. 128-133).
Silica sulfuric acid as an efficient and reusable heterogeneous catalyst have been used for the preparation of 2 H-indazolo[2,1- b]phthalazine-1,6,11(13 H)-trione derivatives from the three-component condensation reaction of phthalhydrazide, dimedone, and aromatic aldehydes under solvent-free conditions in good to excellent yields and short reaction times.▪Silica sulfuric acid as an efficient and reusable heterogeneous catalyst have been used for the preparation of 2 H-indazolo[2,1- b]phthalazine-1,6,11(13 H)-trione derivatives from the three-component condensation reaction of phthalhydrazide, dimedone, and aromatic aldehydes under solvent-free conditions in good to excellent yields and short reaction times.
Keywords: Silica sulfuric acid; Heterogeneous catalyst; Solvent-free; 2; H; -Indazolo[2,1-; b; ]phthalazine-triones; Phthalhydrazide
Fischer–Tropsch synthesis over cobalt catalyst supported on carbon nanotubes in a slurry reactor by Ahmad Tavasoli; Reza M. Malek Abbaslou; Mariane Trepanier; Ajay K. Dalai (pp. 134-142).
The potential of carbon nanotubes (CNTs) supported cobalt catalysts for Fischer–Tropsch (FT) reaction is discussed in this paper. Cobalt on carbon nanotube catalysts were prepared using the wet impregnation method with cobalt loading varying from 15 to 40wt.%. The catalysts were characterized by BET, X-ray diffraction (XRD), H2 chemisorption, TPR, and transmission electron microscopy (TEM). The activity and selectivity of the catalysts were assessed using a continuous stirred tank reactor (CSTR). Most of the cobalt particles were homogeneously distributed inside the tubes and the rest on the outer of the CNTs. Carbon nanotubes as cobalt catalyst support was found to shift the reduction temperature of cobalt oxide species to lower temperatures. The strong metal–support interactions are reduced to a large extent and the reducibility of the catalysts improved significantly. CNT aided in well dispersion of metal clusters and average cobalt clusters size decreased. The hydrocarbon yield in the FT process obtained by CNT-supported cobalt catalyst is about 75% more than that obtained using cobalt on alumina supports. The maximum concentration of active surface Co° sites and FTS activity for CNT-supported catalysts are achieved at 40wt.% cobalt loading. CNT caused a slight decrease in FTS product distribution to lower molecular weight hydrocarbons.Co/CNT catalysts for FTS were prepared with loading varying from 15 to 40wt.%. Most of the cobalt particles were homogeneously distributed inside the tubes. CNT aided in well dispersion of metal clusters and average cobalt clusters size decreased. The FTS rate obtained by Co/CNT is about 75% more than that obtained by Co/Al2O3. The maximum FTS activity is achieved at 40wt.%. CNT caused a slight decrease in FTS product distribution to lower molecular weight hydrocarbons.▪
Keywords: Fischer–Tropsch; Cobalt; Carbon nanotube; Catalyst characterization
Study of the citral/acetone reaction on Mg yAlO x oxides: Effect of the chemical composition on catalyst activity, selectivity and stability by V.K. Díez; J.I. Di Cosimo; C.R. Apesteguía (pp. 143-151).
The liquid-phase citral/acetone reaction was studied on MgO, Al2O3 and Mg yAlO x mixed oxides. The rate of the citral/acetone cross-aldolization to pseudoionones increased linearly with the density of strong O2− base sites. In contrast, the initial rate of the parallel acetone self-condensation reaction augmented with the density of Lewis acid sites.▪The liquid-phase citral/acetone reaction was studied on MgO, Al2O3 and Mg yAlO x mixed oxides with Mg/Al molar ratios of 0.11–3. The density, strength and nature of surface acid sites were determined by NH3 thermodesorption and FTIR of pyridine. The surface basic properties were probed by temperature-programmed desorption of CO2. The rate of the citral/acetone cross-aldolization to pseudoionones increased linearly with the density of strong O2− base sites. Thus, the pseudoionone synthesis was efficiently promoted on MgO and Mg-rich Mg yAlO x samples. In contrast, the initial rate of the parallel acetone self-condensation reaction increased with the density of Lewis acid sites, and diacetone alcohol was more rapidly formed on Al2O3 and Al-rich Mg yAlO x samples. Differences in the reactant adsorption strength on surface Al3+ sites may explain the observed differences between the acid-catalyzed mechanisms of cross- and self-aldolization reactions. In situ catalyst deactivation was determined by performing two consecutive catalytic runs. The activity decay of Mg yAlO x samples during the citral/acetone reaction was between 15 and 20%, irrespective of the catalyst composition.
Keywords: Citral/acetone reaction; Mg; y; AlO; x; catalysts; Aldol condensation; Pseudoionone synthesis; Fine chemicals
MD//Mo and MD//W [MD=Mn, Fe, Co, Ni, Cu and Zn] promotion via spillover hydrogen in hydrodesulfurization by M. Villarroel; P. Baeza; N. Escalona; J. Ojeda; B. Delmon; F.J. Gil-Llambías (pp. 152-157).
The promotion effect of Mn, Fe, Co, Ni, Cu and Zn sulfides on the hydrodesulfurization (HDS) activity of Mo and W sulfides, under experimental conditions like industrial ones, using staked beds, was studied. Synergism between staked beds in all the studied pairs, with a magnitude that leads a volcano curve with a maximum in Co and Ni sulfides was detected. Promotion was well explained by the formation of spillover hydrogen (Hso) in the first bed (in which Mn, Fe, Co, Ni, Cu or Zn sulfides supported on γ-Al2O3 were located) that migrate to the second bed (in which Mo or W sulfides supported on γ-Al2O3 were located), 5mm below. ▪The promotion effect of Mn, Fe, Co, Ni, Cu and Zn sulfides on the hydrodesulfurization (HDS) activity of Mo and W sulfides, under experimental conditions like industrial ones, using staked beds, was studied. Synergism between staked beds in all the studied pairs, with a magnitude that leads a volcano curve with a maximum in Co and Ni sulfides was detected. Promotion was well explained by the formation of spillover hydrogen (Hso) in the first bed (in which Mn, Fe, Co, Ni, Cu or Zn sulfides supported on γ-Al2O3 were located) that migrate to the second bed (in which Mo or W sulfides supported on γ-Al2O3 were located), 5mm below.
Keywords: Spillover hydrogen; Hydrotreating; Promotion effect; Volcano curves
Regioselective mononitration of aromatic compounds using Brønsted acidic ionic liquids as recoverable catalysts by Dong Fang; Qun-Rong Shi; Jian Cheng; Kai Gong; Zu-Liang Liu (pp. 158-163).
Some novel acyclic Brønsted acidic task-specific ionic liquids (TSILs) that bear an alkane sulfonic acid group in an acyclic trialkanylammonium cation were synthesized and their uses as halogen-free catalysts for regioselective mononitration of aromatic compounds were investigated. The reactions were carried out at 60–80°C with reasonable to good yields and improved para-selectivities for halogenobenzenes compared to those in the absence of the catalysts. In addition, the TSILs could be recovered and reused without noticeably decreasing the catalytic activity.The regioselective mononitration of aromatic compounds was carried out at 60–80°C, catalyzed by recyclable acyclic Brønsted acidic task-specific ionic liquids that bear an alkane sulfonic acid group in an acyclic trialkanylammonium cation with reasonable to good yields. Para-selectivities for halogenobenzenes were improved compared to those in the absence of the catalysts.▪
Keywords: Ionic liquid; Catalyst; Nitration reaction
Effect of pretreatment conditions on the catalytic performance of Ni-Pt-W supported on amorphous silica-alumina catalysts by Miloud Guemini; Yacine Rezgui (pp. 164-175).
Activation procedures of Ni-W-Pt based catalysts, prepared by means of an hybrid technique: sol–gel and incipient wetness impregnation, were investigated in terms of their activity in reaction of n-hexane isomerization in a continuous fixed-bed quartz reactor operating at atmospheric pressure, by changing operating conditions such as time on stream, SiO2/Al2O3 and H2/ n-hexane ratios. This study aims to understand the effects of the pretreatment conditions, such as calcination and reduction temperature, over some properties of these catalysts and to analyze the relationship between the metal content, the acidity (strength) of the samples and their catalytic performance.The chemical composition of the prepared solids have been characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), their specific surface areas were measured using BET method, while their reduction behavior was characterized by temperature-programmed reduction and their acidity was assessed by means of ammonia temperature-programmed desorption. The collected data revealed that both BET surface areas and catalytic activity as well as surface acidity of these solids are strongly dependent on their pretreatment conditions. Besides, the reduction behavior of the prepared materials was related to nickel and platinum amounts, the higher the concentrations of these species the easier the reducibility of the samples. On the other hand, it was found that all (Ni xPt y) catalysts deactivate with time on stream, with the conversion remaining steady after 100min. Moreover, the obtained results on (Ni12Pt0,4)AC catalyst showed that the SiO2/Al2O3 ratio and H2 partial pressure affect isomerization selectivity while positively opposite effect was observed for activity (conversion). In addition, the main products in n-hexane hydroconversion were found to be monobranched isomers which dominate all practical conversions and their formation increases together with that of multibranched ones. Besides, the cracked products are not produced in significant amounts until about 30% conversion. ▪Activation procedures of Ni-W-Pt based catalysts, prepared by means of a hybrid technique: sol–gel and incipient wetness impregnation, were investigated in terms of their activity in reaction of n-hexane isomerization in a continuous fixed-bed quartz reactor operating at atmospheric pressure, by changing operating conditions such as time on stream, SiO2/Al2O3 and H2/ n-hexane ratios. This study aims to understand the effects of the pretreatment conditions, such as calcination and reduction temperature, over some properties of these catalysts and to analyze the relationship between the metal content, the acidity (strength) of the samples and their catalytic performance.The chemical composition of the prepared solids have bas characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), their specific surface areas were measured using BET method, while their reduction behavior was characterized by temperature-programmed reduction and their acidity was assessed by means of ammonia temperature-programmed desorption. The collected data revealed that both BET surface areas and catalytic activity as well as surface acidity of these solids are strongly dependent on their pretreatment conditions. Besides, the reduction behavior of the prepared materials was related to nickel and platinum amounts, the higher the concentrations of these species the easier the reducibility of the samples. On the other hand, it was found that all (Ni xPt y) catalysts deactivate with time on stream, with the conversion remaining steady after 100min. Moreover, the obtained results on (Ni12Pt0,4)AC catalyst showed that the SiO2/Al2O3 ratio and H2 partial pressure affect isomerization selectivity positively while opposite effect was observed for activity (conversion). In addition, the main products in n-hexane hydroconversion were found to be monobranched isomers which dominate all practical conversions and their formation increases together with that of multibranched ones. Besides, the cracked products are not produced in significant amounts until about 30% conversion.
Keywords: Platinum; Tungsten-oxide; Nickel; Isomerization; Pretreatment conditions; Hybrid technique
Effect of reduction pressure on precipitated potassium promoted iron–manganese catalyst for Fischer–Tropsch synthesis by Mingyue Ding; Yong Yang; Jian Xu; Zhichao Tao; Hulin Wang; Hong Wang; Hongwei Xiang; Yongwang Li (pp. 176-184).
Effects of reduction pressure in syngas (H2/CO=1.2), on the textural properties and bulk/surface phase compositions of a precipitated potassium promoted iron–manganese catalyst, were investigated by N2 physisorption, X-ray diffraction (XRD), Mössbauer effect spectroscopy (MES), temperature-programmed hydrogenation (TPH) and X-ray photoelectron spectroscopy (XPS). Fischer–Tropsch synthesis (FTS) was performed in a slurry-phase continuously stirred tank reactor (STSR). The characterization results indicated that the increase of reduction pressure led to the decrease in surface area and increase in pore diameter. Pretreatment at higher reduction pressure promoted the reduction of α-Fe2O3 to Fe3O4 and enhanced the Boudouard reaction, whereas suppressed the carburization of magnetite. The increase of carbonaceous species concentration with increasing reduction pressure resulted in the decrease in amounts of magnetite and carbide phases in the near-surface region. In the FTS reaction, the catalytic activity of the catalyst decreased gradually and the product distribution shifted towards lower molecular weight hydrocarbons with the increase in reduction pressure. In addition, the selectivity to olefins decreased and the selectivity to oxygenates increased with increasing reduction pressure.The change of reduction pressure has obvious influence on the textural properties, bulk/surface phase compositions, and catalytic performances of precipitated potassium promoted iron–manganese catalysts. The increase in reduction pressure causes a decrease in amounts of Fe3O4 and iron carbides, and an increase in the amount of carbonaceous deposits in the near-surface region of the catalyst.▪
Keywords: Fischer–Tropsch synthesis; Iron–manganese catalyst; Reduction pressure; Mössbauer effect spectroscopy
New Mo-Fe-O silica supported catalysts for methanol to formaldehyde oxidation by Ana Paula Soares Dias; V.V. Rozanov; João Carlos Bentes Waerenborgh; Manuel Farinha Portela (pp. 185-194).
Silica supported Mo-Fe and Mo-Fe-P mixed oxides (Mo/Fe=3 atomic ratio) were prepared in the presence of citric acid as chelating agent to obtain a uniform distribution of the active phase. Loading of 23.1% (w/w) of MoO3 was used exceeding the monolayer content (around 2.2 monolayers of MoO3). The low interaction between the silica and the mixed oxide in addition to the high content of the active phase led to a three-dimensional distribution of the active phase, confirmed by SEM.Several iron (Fe3+) precursors (nitrate, chloride, sulfate, phosphate and pyrophosphate) were used in order to assess their effect on the catalysts performances.Some elements (N, Cl, S and P) from the iron precursors remained in the catalyst. Samples prepared from phosphate and pyrophosphate had phosphorus in their compositions and Mössbauer spectra revealed the presence of iron phosphate. Nevertheless, due to lack of crystallinity, these phases (iron phosphates) are probably inactive.All the prepared catalysts display high activity and selectivity towards formaldehyde, even for low and high methanol conversions. The catalyst prepared from iron pyrophosphate was the most active. The presence of heteropolymolybdates, containing phosphorus, or its Mo rich surface can perhaps explain its enhanced catalytic behavior. For temperatures lower than 625K this sample (merely 26.2% (w/w) of active phase) presented higher formaldehyde yields than one unsupported industrial catalyst. Such a catalyst prepared from iron pyrophosphate presents promising catalytic performances for use in fluidized bed reactors.The loss of Mo during reaction was observed for all the prepared catalysts. Micrographs for post reaction samples displayed MoO3 needles (or plates) formed during the redox cycle, which are easily sublimated. Conversely, for the sample prepared from iron pyrophosphate the MoO3 needles are absent, which is probably indicative of a different reaction mechanism.Silica supported Mo-Fe and Mo-Fe-P mixed oxides (Mo/Fe=3 atomic ratio) were prepared in the presence of citric acid as chelating agent to obtain a uniform distribution of the active phase. Several iron (Fe3+) precursors (nitrate, chloride, sulfate, phosphate and pyrophosphate) were used in order to assess their effect on the catalysts performances. The catalyst prepared from iron pyrophosphate was the most active. The presence of heteropolymolybdates, containing phosphorus, or its Mo rich surface can perhaps explain its enhanced catalytic behavior. The loss of Mo during reaction was observed for all the prepared catalysts. Micrographs for post reaction samples displayed MoO3 needles (or plates) formed during the redox cycle, which are easily sublimated. ▪
Keywords: Supported catalysts; Iron molybdates; Silica; Methanol oxidation; Formaldehyde; Iron phosphates
Titanium and cerium-containing mesoporous silicate materials as catalysts for oxidative cleavage of cyclohexene with H2O2: A comparative study of catalytic activity and stability by M.N. Timofeeva; O.A. Kholdeeva; S.H. Jhung; J.-S. Chang (pp. 195-200).
Adipic acid can be obtained with the yield of 18 and 33% over transition-metal-containing silicate materials Ti-MMM-2 and Ce-SBA-15, respectively, via oxidative cleavage of cyclohexene with aqueous H2O2. Both high concentration of the oxidant and polar reaction products lead to irreversible catalysts deactivation. ▪Catalytic properties of transition-metal-containing silicate materials with hexagonally packed mesopore-channels, Ti-MMM-2 and Ce-SBA-15, have been studied in oxidative cleavage of cyclohexene (CyH) to adipic acid using aqueous H2O2 as oxidant. In a solvent-free system, the yield of adipic acid reached 10–15% at H2O2/CyH 3.6molmol−1 and 80°C after 72h. The stepwise addition of the oxidant to the reaction mixture allowed increasing the yield of the target product up to 33 and 18% for Ti-MMM-2 and Ce-SBA-15, respectively. For both catalysts, the yield of adipic acid decreased significantly in the second run despite CyH conversion attained 100%. The catalyst stability and the reasons of the deactivation have been explored. For both catalytic materials, partial decrease of the mesopore surface area and mesopore volume was observed after the CyH oxidation run. DRS–UV–vis study revealed irreversible formation of oligomerized TiO2-like species on the Ti-MMM-2 surface due to interaction of Ti centres with the oxidant and the reaction products. The elemental analysis data showed that adipic acid causes leaching of titanium from Ti-MMM-2 into solution. Ce-SBA-15 was found to be more stable with respect to the active metal leaching but prone to deactivation due to agglomeration of cerium ions to form cerium oxide nanocrystallites; partial reduction of Ce(IV) to Ce(III) also occurred.
Keywords: Cyclohexene; Oxidation; Hydrogen peroxide; Adipic acid; Titanium; Cerium; Mesoporous silicate materials
Catalytic hydrogenation of linoleic acid to stearic acid over different Pd- and Ru-supported catalysts by P. Mäki-Arvela; J. Kuusisto; E.Mateos Sevilla; I. Simakova; J.-P. Mikkola; J. Myllyoja; T. Salmi; D.Yu. Murzin (pp. 201-212).
Catalytic hydrogenation of linoleic acid in n-decane as a solvent was studied over several Pd- and Ru-supported catalysts in order to achieve complete conversion of linoleic acid into stearic acid. ▪Catalytic hydrogenation of linoleic acid in n-decane as a solvent was studied over several Pd- and Ru-supported catalysts in order to achieve complete conversion of linoleic acid into stearic acid. Catalyst deactivation by coking was, however, rather prominent. Supported ruthenium, was more prone to deactivation than palladium, which was also confirmed in the catalyst reuse tests with technical grade linoleic acid. The mesoporous structure of the catalyst was preferable to achieve fast hydrogenation of the intermediate products, thus promoting formation of stearic acid.
Keywords: Hydrogenation; Linoleic acid; Supported metals; Palladium; Ruthenium
Topological analysis of catalytic reaction networks: Water gas shift reaction on Cu(111) by Caitlin A. Callaghan; Saurabh A. Vilekar; Ilie Fishtik; Ravindra Datta (pp. 213-232).
This paper describes our new reaction route network approach for elucidating reaction mechanisms and kinetics of complex catalytic reactions, which is applied to water gas shift reaction on Cu(111) comprising 19 elementary reaction steps along with detailed kinetics. Three dominant pathways are found, eventually, yielding an 11-step simplified mechanism, from which a predictive rate expression is derived. This provides good agreement not only with the complete WGS mechanism, but also with our experimental data on Cu.Microkinetic mechanism vs. experimental data for Cu under the following experimental conditions: catalyst loading of 0.14g/cm3; total feed flow rate of 236cm3 (STP)min−1; pressure of 1.5atm; residence time τ=1.8s; feed composition of H2O(10%), CO(10%) and N2(balance). ▪New catalysts are being sought for the water gas shift (WGS) reaction in connection with distributed hydrogen generation. This quest would be aided by improved fundamental understanding of WGS catalysis. We, thus, present here a systematic theoretical approach, namely, Reaction Route (RR) Graph analysis, for developing a comprehensive understanding of the WGS reaction based on a detailed molecular mechanism with a priori kinetics. The RR Graphs follow flow network laws of Kirchhoff, so that they allow not only graphical depiction of the myriad pathways, but also a detailed flux analysis of the network. Thus, we utilize a 19-step mechanism and assemble it into a RR Graph, which is analogous to an equivalent electrical circuit. These steps were picked to be comprehensive without causing undue complexities. A simplification and pruning of the mechanism is then performed based on Kirchhoff's laws of current (rate) and potential (affinity). As a result, the dominant pathways as well as the rate-limiting steps become transparent. Three dominant pathways are found, eventually, yielding an 11-step simplified mechanism, from which a predictive rate expression is derived. This provides good agreement not only with the complete WGS mechanism, but also with our own experimental data on Cu. Prediction of WGS activity on other metals is also provided.
Keywords: Water gas shift reaction; Graph theory; Reaction network; Reaction pathways; Electrical analog; Kirchhoff's laws
A comparative study of the WO x dispersion on Mn-promoted tungstated zirconia catalysts prepared by conventional and high-throughput experimentation by M.L. Hernández-Pichardo; J.A. Montoya; P. del Angel; A. Vargas; J. Navarrete (pp. 233-240).
Conventional and high-throughput experimentation (HTE) techniques were used for the synthesis, characterization, and catalytic testing of Pt/Mn–WO x–ZrO2 materials. The catalysts were prepared by surfactant-assisted coprecipitation and screened for catalytic activity in a multi-channel fixed bed (MCFB) micro-reactor for the hydroisomerization of n-hexane. Conventional coprecipitation route leads mainly to the segregation of the WO3 crystalline phase (XRD). On the other hand, the use of the automated HTE route allows the formation of catalysts with a highly dispersed WO x phase on the zirconia surface and a high surface area (60–100m2/g) when calcined at 800°C (N2 physisorption, XRD, Raman, UV–vis, HRTEM). These polytungstates with different coordination symmetry are accessible to the reactants and they lead to an increase in the catalytic activity and selectivity to the bi-ramified products (2,2-DMB and 2,3-DMB) in the n-hexane isomerization. In addition, it was found that the incorporation of Mn modifies the nanostructural properties of the tungstated zirconia favoring the catalytic activity of these materials.Conventional and high-throughput experimentation techniques were used to investigate the catalytic behavior of Pt/WO x–ZrO2 catalysts modified with Mn in the hydroisomerization of n-hexane. The use of the automated HTE route allows the formation of highly dispersed WO x catalysts with high surface area. These polytungstates increase the catalytic activity and selectivity. The incorporation of Mn also promotes the catalytic activity.▪
Keywords: High-throughput experimentation; Tungstated zirconia; Surfactant; Tungsten surface density; n; -Hexane hydroisomerization
One-step synthesis of noble metal–titanium dioxide nanocomposites in a flame aerosol reactor by Vinay Tiwari; Jingkun Jiang; Virendra Sethi; Pratim Biswas (pp. 241-246).
Noble metal–titanium dioxide nanocomposites were synthesized in one step using a flame aerosol reactor. Nanocomposite properties (such as specific surface area, crystal phase, and morphology) were varied by controlling the multiple species aerosol growth dynamics (nucleation, coagulation and sintering). Higher photocatalytic activities were achieved in noble metal–titanium dioxide nanocomposites compared to pristine titanium dioxide. ▪Noble metal–titanium dioxide nanocomposites (Pt/TiO2, Pd/TiO2 and bimetallic Pt-Pd/TiO2) were synthesized in one step using a flame aerosol reactor (FLAR). The specific surface area, crystal phase and morphology of the nanocomposites were controlled by adjusting the reactant concentration and the temperature–time history in the reactor. The synthesized nanomaterials were characterized using transmission electron microscopy (TEM), electron diffraction, X-ray diffraction (XRD) and nitrogen adsorption (BET). Nanocomposites with 0.5–3.0% (wt%) noble metal loading were synthesized. Nanosized noble metal particles (2–4nm) were dispersed on the 30–40nm TiO2 surface with an overall specific surface area in the range of 40–60m2/g. The specific surface area increased with increasing noble metal loading. For the chosen flame conditions, a mixture of anatase and rutile phase was obtained without noble metal addition. On incorporation of the noble metal, the formation of the rutile phase of titanium dioxide was suppressed. The synthesized nanocomposites were tested for the photocatalytic oxidation of methyl orange dye in an aqueous phase. Platinum particles dispersed on the TiO2 surface enhanced the photocatalytic activity compared to pristine TiO2. The existence of an optimum platinum loading for the highest photocatalytic activity was confirmed, and was approximately 0.5–1.0% Pt. Palladium addition had a detrimental effect on the photocatalytic activity of titanium dioxide. Bimetallic noble metal catalysts (Pt-Pd/TiO2) showed enhanced photocatalytic activity compared to pristine titanium dioxide, but lower than platinum (only)–titanium dioxide nanocomposites.
Keywords: Flame synthesis; Platinum; Palladium; TiO; 2; nanoparticle; Photocatalysis