Sintering Behavior of TiO2-Supported Model Cobalt Fischer–Tropsch Catalysts under H2 Reducing Conditions and Elevated Temperature

Xaba, Bongani Michael; Villiers, J. P. R. de

doi:10.1021/acs.iecr.6b02311

Cited by 20 publications

(25 citation statements)

References 34 publications

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“…Further, 1% Pd/P25-TiO 2 also shows a broad reduction peak at high-temperature 392 °C consuming 6.4 mL/g H 2, and this peak may be attributed to the reduction of Ti 4+ to Ti 3+ . A similar observation was reported for P25-TiO 2 by Xaba et al [37]. TiO 2, upon calcination in the H 2 atmosphere, creates oxygen vacancies (O v ) in its lattice.…”

Section: Resultssupporting

confidence: 84%

Pd Supported Catalysts with Intrinsic Surface Electropositive Sites for Improved Selective Hydrogenation of Cinnamaldehyde

Vatti¹,

Krishnamurthy²,

Viswanathan³

2020

Preprint

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Uniform-spherical Pd nanoparticles (NPs) supported catalysts were prepared by a mild-temperature chemical reduction method. Pd colloidal suspension was wet-impregnated on various supports, P25-TiO2, SiO2, and γ-Al2O3. In XPS, asymmetric Pd 3d5/2 peak reveals % surface concentration of Pd2+ and Pd0 species. The surface Pd2+/Pd0 ratio on the catalyst surface varied between ~1 to 0.15 depending on strong-metal support interactions (SMSI) inferred from XPS and H2-TPR studies. A linear correlation between Pd2+/Pd0 ratio and turnover frequency (TOF) was observed, with 1% Pd/P25-TiO2 showing the highest TOF/selectivity with Pd2+/Pd0 ratio ~1.0, whereas 1% Pd/γ-Al2O3 showed the lowest TOF/selectivity with lowest Pd2+/Pd0 ratio 0.15. Interestingly, H2-TPR reveals PdH decomposition peaks along with the Ti4+ reduction peak, and XPS Ti 2p of 1% Pd/P25-TiO2 indicates the presence of Ti3+ in TiO2 lattice, which may have generated due to H2-spillover from Pd to P25-TiO2. Hence, we observed excellent COL selectivity (~90%) and 100 % conversion with 1.5% Pd/P25-TiO2 catalyst. Excellent COL selectivity may be ascribed to small Pd NPs (~3 nm) with intrinsic surface electropositive sites (Pd2+) created by partial reduction on the catalyst surface along with SMSI. These electropositive sites (Pd2+) promote preferential C=O adsorption. On the other hand, post-reduced catalyst in H2 @300 °C (1% Pd/P25-TiO2-PRH2) with large Pd NPs (~7 nm) showed significant selectivity loss (>50 %), which confirm significance of small Pd NPs with electropositive sites.

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Section: Resultssupporting

confidence: 84%

Pd Supported Catalysts with Intrinsic Surface Electropositive Sites for Improved Selective Hydrogenation of Cinnamaldehyde

Vatti¹,

Krishnamurthy²,

Viswanathan³

2020

Preprint

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“…TPR analysis reveals two reduction peaks common for all studied samples centered at 350°C and 480-500°C. According to the literature, the reduction of Co 3 O 4 species on a TiO 2 surface is a 2-step process involving the consecutive reduction of Co(III) to Co(II) and Co(II) to metallic Co [21,23,24]. Therefore, a first peak at about 350°C is expected to occur due to the reduction of Co 3 O 4 to CoO, followed by a second peak at 450-500°C attributed to the reduction of CoO to metallic Co.…”

Section: Physico-chemical Characterization Of the Co 3 O 4 /Tio 2 Andmentioning

confidence: 99%

Sonocatalytic oxidation of EDTA in aqueous solutions over noble metal-free Co3O4/TiO2 catalyst

Parizot

Chave

Gálvez

et al. 2019

Applied Catalysis B: Environmental

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The sonocatalytic degradation of EDTA in aqueous solution was studied under ultrasound irradiation (345 kHz, 73 W, acoustic power 0.20 W•mL −1 , Ar and Ar/O 2 saturating gases, T = 20-50°C) in the presence of Co 3 O 4 /TiO 2 and Pt/TiO 2 nanocatalysts. About 90% of EDTA (C 0 = 5 10-3 M) was oxidized during ultrasonic treatment at 40°C in the presence of the Co 3 O 4 /TiO 2 catalyst and Ar/O 2 gas mixture. By contrast, Pt/TiO 2 catalyst exhibited much lower sonocatalytic activity in this system. Suggested mechanism of EDTA oxidation in the presence of Co 3 O 4 /TiO 2 catalyst involved the generation of oxidizing radicals by acoustic cavitation and Co(II)-Co(III) redox process. Quite low apparent activation energy of the sonocatalytic process (E a = 19 kJ mol −1) was attributed to diffusion of reagents in the vicinity of the active sites of catalyst. Sonocatalytic degradation of EDTA is accompanied by formation of iminodiacetic acid, formic acid, oxalic acid, glycolic acid and acetic acid as intermediate products in an agreement with radical-driven mechanism.

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“…This rationalizes the experimental observation of the smaller Pt NPs on r-TiO 2 than that on a-TiO 2 after the calcination at 773 K, 30 and the evident growth of Pt on a-TiO 2 NPs at 673 K. 81 This explains the better stability and low ripening tendency found in Ru/TiO 2 33,34 and Co/TiO 2 as well. 35 3.3.1. Anatase Titanium Oxide.…”

Section: Resultsmentioning

confidence: 99%

Influence of Crystal Facet and Phase of Titanium Dioxide on Ostwald Ripening of Supported Pt Nanoparticles from First-Principles Kinetics

Wan

Dai

et al. 2019

J. Phys. Chem. C

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Metal oxide plays an important role on stability and catalytic performance of supported metal nanoparticles, but mechanistic understanding of structure sensitivity and optimization of the oxide supports remains elusive in heterogeneous catalysis. Taking Ostwald ripening of platinum nanoparticles supported on titanium dioxide (TiO2) as an example, we reveal here a great structure sensitivity of oxide facets and crystal phases on sintering of supported metal nanoparticles through first-principles kinetic simulation. Total activation energies of the Pt ripening on various pristine TiO2 surfaces of both anatase and rutile phases are calculated by density functional theory, and Ostwald ripening under isothermal condition and temperature programmed condition are simulated numerically. Calculated total activation energies are found inversely proportional to the corresponding oxide surface energies, and vary considerably from 1.76 to 3.56 eV. The Pt ripening rate on the pristine TiO2 surfaces follows the order of r(001) ≈ a(001) ≫ a(100) ≈ r(101) > r(100) > a(101) ≈ r(110). For TiO2 support exposing different facets, not only their intrinsic ripening rate but also their relative surface area determines the overall ripening kinetics and formation of transit bimodal particle size distribution. For pristine anatase TiO2 exposing a(001) and a(101) facets, ripening starts on a(101) facets only after ripening on a(001) facets finishes due to their order of magnitude difference in ripening rate, resulting a step-wise increase of average particle size with ripening time. For pristine rutile TiO2 exposing r(101) and r(110) facets, ripening could proceed simultaneously on both facets due to their modest difference in ripening rate, and the average particle size increases monotonically with ripening time. Compared to rutile TiO2, anatase TiO2 supports are less resistant to the metal nanoparticles ripening since a(001) facets with high ripening rate is likely to be exposed. The present work is compared to available experiments and the theoretical framework established could be expanded to various metal and oxide systems.

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Sintering Behavior of TiO₂-Supported Model Cobalt Fischer–Tropsch Catalysts under H₂ Reducing Conditions and Elevated Temperature

Cited by 20 publications

References 34 publications

Pd Supported Catalysts with Intrinsic Surface Electropositive Sites for Improved Selective Hydrogenation of Cinnamaldehyde

Pd Supported Catalysts with Intrinsic Surface Electropositive Sites for Improved Selective Hydrogenation of Cinnamaldehyde

Sonocatalytic oxidation of EDTA in aqueous solutions over noble metal-free Co3O4/TiO2 catalyst

Influence of Crystal Facet and Phase of Titanium Dioxide on Ostwald Ripening of Supported Pt Nanoparticles from First-Principles Kinetics

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