Oxygenate Reactions over PdCu and PdAg Catalysts: Distinguishing Electronic and Geometric Effects on Reactivity and Selectivity

2020 ◽  
Author(s):  
Tanmayi Bathena ◽  
Truc Phung ◽  
Scott Svadlenak ◽  
Yu Liu ◽  
Lars Grabow ◽  
...  
Keyword(s):  
Metallic Nanoparticles ◽  
Reaction Rate ◽  
Theoretical Calculations ◽  
Catalyst System ◽  
Bifunctional Catalyst ◽  
Ligand Effects ◽  
Hydrogenation Reactions ◽  
Ensemble Effects ◽  
Electron Donation ◽  
Geometric Effects

We investigate PdCu and PdAg catalysts in the context of oxygenate upgrading for biofuels. To this end, we measure the rates of decarbonylation and hydrogenation of butyraldehyde, the reactive intermediate for the industrially relevant Guerbet condensation, and correlate the selectivity and reactivity with the properties of the catalysts via a range of characterization efforts. Data obtained from EXAFS and XANES show that the bulk of the catalyst metallic nanoparticles is enriched in Pd, while the surface is enriched in Cu and Ag. The data for PdCu show clear dominance of geometric (ensemble) effects on the selectivity. Conversely, the electronic (ligand) effects of alloying dominate over the reaction rate of the catalysts, as electron donation from Cu to Pd promotes the Cu and increases the desired (de)hydrogenation reactions. In contrast, in PdAg catalysts, the weaker electronic exchange, as indicated by Pd L edge XANES and theoretical calculations, is not sufficient to promote Ag, resulting in monotonic loss of activity with increasing Ag content and without selectivity improvement. We use the implications of these findings to provide valuable design principles for oxygenate catalysis and to discover a highly selective bifunctional catalyst system, comprised of a PdCu alloy catalyst and titanium dioxide for the upgrading of ethanol to longer-chain oxygenates.<br>

Oxygenate Reactions over PdCu and PdAg Catalysts: Distinguishing Electronic and Geometric Effects on Reactivity and Selectivity

2020 ◽  
Author(s):  
Tanmayi Bathena ◽  
Truc Phung ◽  
Scott Svadlenak ◽  
Yu Liu ◽  
Lars Grabow ◽  
...  
Keyword(s):  
Metallic Nanoparticles ◽  
Reaction Rate ◽  
Theoretical Calculations ◽  
Catalyst System ◽  
Bifunctional Catalyst ◽  
Ligand Effects ◽  
Hydrogenation Reactions ◽  
Ensemble Effects ◽  
Electron Donation ◽  
Geometric Effects

We investigate PdCu and PdAg catalysts in the context of oxygenate upgrading for biofuels. To this end, we measure the rates of decarbonylation and hydrogenation of butyraldehyde, the reactive intermediate for the industrially relevant Guerbet condensation, and correlate the selectivity and reactivity with the properties of the catalysts via a range of characterization efforts. Data obtained from EXAFS and XANES show that the bulk of the catalyst metallic nanoparticles is enriched in Pd, while the surface is enriched in Cu and Ag. The data for PdCu show clear dominance of geometric (ensemble) effects on the selectivity. Conversely, the electronic (ligand) effects of alloying dominate over the reaction rate of the catalysts, as electron donation from Cu to Pd promotes the Cu and increases the desired (de)hydrogenation reactions. In contrast, in PdAg catalysts, the weaker electronic exchange, as indicated by Pd L edge XANES and theoretical calculations, is not sufficient to promote Ag, resulting in monotonic loss of activity with increasing Ag content and without selectivity improvement. We use the implications of these findings to provide valuable design principles for oxygenate catalysis and to discover a highly selective bifunctional catalyst system, comprised of a PdCu alloy catalyst and titanium dioxide for the upgrading of ethanol to longer-chain oxygenates.<br>

scholarly journals Oxygenate Reactions over PdCu and PdAg Catalysts: Distinguishing Electronic and Geometric Effects on Reactivity and Selectivity

2020 ◽  
Author(s):  
Tanmayi Bathena ◽  
Truc Phung ◽  
Scott Svadlenak ◽  
Yu Liu ◽  
Lars Grabow ◽  
...  
Keyword(s):  
Metallic Nanoparticles ◽  
Reaction Rate ◽  
Theoretical Calculations ◽  
Catalyst System ◽  
Bifunctional Catalyst ◽  
Ligand Effects ◽  
Hydrogenation Reactions ◽  
Ensemble Effects ◽  
Electron Donation ◽  
Geometric Effects

We investigate PdCu and PdAg catalysts in the context of oxygenate upgrading for biofuels. To this end, we measure the rates of decarbonylation and hydrogenation of butyraldehyde, the reactive intermediate for the industrially relevant Guerbet condensation, and correlate the selectivity and reactivity with the properties of the catalysts via a range of characterization efforts. Data obtained from EXAFS and XANES show that the bulk of the catalyst metallic nanoparticles is enriched in Pd, while the surface is enriched in Cu and Ag. The data for PdCu show clear dominance of geometric (ensemble) effects on the selectivity. Conversely, the electronic (ligand) effects of alloying dominate over the reaction rate of the catalysts, as electron donation from Cu to Pd promotes the Cu and increases the desired (de)hydrogenation reactions. In contrast, in PdAg catalysts, the weaker electronic exchange, as indicated by Pd L edge XANES and theoretical calculations, is not sufficient to promote Ag, resulting in monotonic loss of activity with increasing Ag content and without selectivity improvement. We use the implications of these findings to provide valuable design principles for oxygenate catalysis and to discover a highly selective bifunctional catalyst system, comprised of a PdCu alloy catalyst and titanium dioxide for the upgrading of ethanol to longer-chain oxygenates.<br>

Hydrogenation of Para-Nitrotoluene on Catalytic Systems Containing Oxides of Rare Earth Elements

2021 ◽  
Vol 410 ◽  
pp. 389-393
Author(s):  
Galina M. Kurunina ◽  
Olga M. Ivankina ◽  
Gennady M. Butov
Keyword(s):  
Rare Earth ◽  
Reaction Rate ◽  
High Selectivity ◽  
Nitro Compounds ◽  
Aqueous Alcohol ◽  
Hydrogenation Rate ◽  
Catalytic Systems ◽  
Liquid Phase Hydrogenation ◽  
Aqueous Alcohol Solutions ◽  
Hydrogenation Reactions

This work is devoted to the study of the activity of 1% platinum catalysts containing rare earth element oxides (OREE) - Gd2O3, Ce2O3 and aluminum oxide as a carrier in the hydrogenation reactions of nitro compounds on the example of n-nitrotoluene. These catalytic systems in the conditions of liquid-phase hydrogenation provide high selectivity of the process and practically quantitative yield. The process was controlled by the potentiometric method, the reaction rate was judged by the amount of hydrogen absorbed per unit time. It is found that 20% and higher aqueous alcohol solutions can be used as a solvent during hydrogenation. It was found that the initial hydrogenation rate for 1% Pt/Gd2O3 is 3.2 times higher, and for 1% Pt/Ce2O3 Cerium it is 1.6 times higher relative to the 1% Pt/Al2O3 comparison catalyst.

Facile assembly of bifunctional, magnetically retrievable mesoporous silica for enantioselective cascade reactions

2019 ◽  
Vol 55 (90) ◽  
pp. 13578-13581 ◽  
Author(s):  
Zhongrui Zhao ◽  
Fengwei Chang ◽  
Tao Wang ◽  
Lijian Wang ◽  
Lingbo Zhao ◽  
...  
Keyword(s):  
Mesoporous Silica ◽  
Cross Coupling ◽  
Bifunctional Catalyst ◽  
Cascade Reactions ◽  
Transfer Hydrogenation ◽  
Asymmetric Transfer Hydrogenation ◽  
Aromatic Alcohols ◽  
Hydrogenation Reactions ◽  
Successive Reduction

A magnetically recyclable bifunctional catalyst enables synergistic Suzuki cross-coupling/asymmetric transfer hydrogenation and successive reduction/asymmetric transfer hydrogenation reactions for the preparation of chiral aromatic alcohols.

scholarly journals Size Matters: New Zintl Phase Hydrides of REGa (RE = Y, La, Tm) and RESi (RE = Y, Er, Tm) with Large and Small Cations

Crystals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 600
Author(s):  
Werwein ◽  
Hansen ◽  
Kohlmann
Keyword(s):  
Density Functional ◽  
Theoretical Calculations ◽  
Structural Diversity ◽  
Type Structure ◽  
Zintl Phases ◽  
Structure Form ◽  
Functional Theory ◽  
X Ray ◽  
Hydrogenation Reactions ◽  
Tetrahedral Voids

Many Zintl phases exhibiting a CrB type structure form hydrides. Systematic studies of AeTtHx (Ae = Ca, Sr, Ba; Tt = Si, Ge, Sn), LnTtHx (Ln = La, Nd; Tt = Si, Ge, Sn), and LnGaHx (Ln = Nd, Gd) showed the vast structural diversity of these systems. Hydrogenation reactions on REGa (RE = Y, La, Tm) and RESi (RE = Y, Er, Tm) were performed in steel autoclaves under hydrogen pressure up to 5 MPa and temperatures up to 773 K. The products were analyzed by X-ray and neutron powder diffraction. RESi (RE = Y, Er, Tm) form hydrides in the C-LaGeD type. LaGaD1.66 is isostructural to NdGaD1.66 and shows similar electronic features. Ga-D distances (1.987(13) Å and 2.396(9) Å) are considerably longer than in polyanionic hydrides and not indicative of covalent bonding. In TmGaD0.93(2) with a distorted CrB type structure deuterium atoms exclusively occupy tetrahedral voids. Theoretical calculations on density functional theory (DFT) level confirm experimental results and suggest metallic properties for the hydrides.

THE ROLE OF ALPHA-KETOLS IN THE LOW-SUGAR REDOX RECIPE FOR LOW TEMPERATURE EMULSION COPOLYMERIZATION

1951 ◽  
Vol 29 (11) ◽  
pp. 949-958
Author(s):  
R. J. Orr ◽  
H. Leverne Williams
Keyword(s):  
Free Radical ◽  
Ferrous Iron ◽  
Reaction Rate ◽  
Catalyst System ◽  
Emulsion Copolymerization ◽  
Peroxy Compounds ◽  
Induced Decomposition ◽  
Amine Compounds ◽  
Better Than

It was found that the induced decomposition of peroxy compounds could lead to faster rates of polymerization or practical rates of polymerization at lower temperatures. In Germany polymerization recipes were developed containing a peroxy compound in the oil phase, a reducer in the aqueous phase and a metal carrier. This idea was transferred to America after the war and became the basis of the present recipes used in the production of cold rubbers. As reducers the most commonly used appear to be digested d-glucose or an excess of ferrous iron but recently the polyamines and other amine compounds have been found to be quite effective. The mixture of amine and sugar was better than either alone. It has been shown that this mixture will function in the presence of reactive monomers such as acrylonitrile. The role of such reducers is of considerable interest so that further studies were undertaken. The results obtained may be illustrated by acetoin. As the amount of acetoin is increased in the recipe the amount of ferrous iron required for maximal conversion in a given time is decreased. This is because at higher than the optimal amounts, although the reaction rate is still increasing, the catalyst system is rapidly exhausted so that the reaction dies at a lower conversion. The data can be explained by assuming formation of free radicals by the induced decomposition of the peroxide either by the acetoin, the ferrous iron, or a complex between the iron and acetoin. This free radical then initiates polymerization. The acetoin free radical residue can induce the further decomposition of the peroxide or possibly can reduce ferric iron to ferrous. Other compounds yield similar results.

Sequential synthesis of β-amino alcohols using a CeO2–ZrO2 bifunctional catalyst system

2013 ◽  
Vol 3 (5) ◽  
pp. 1308 ◽  
Author(s):  
Kalpesh D. Parghi ◽  
Sandip R. Kale ◽  
Sandeep S. Kahandal ◽  
Manoj B. Gawande ◽  
Radha V. Jayaram
Keyword(s):  
Catalyst System ◽  
Amino Alcohols ◽  
Bifunctional Catalyst

scholarly journals Photocatalytic Performance of CuxO/TiO2 Deposited by HiPIMS on Polyester under Visible Light LEDs: Oxidants, Ions Effect, and Reactive Oxygen Species Investigation

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 412 ◽  
Author(s):  
Hichem Zeghioud ◽  
Aymen Assadi ◽  
Nabila Khellaf ◽  
Hayet Djelal ◽  
Abdeltif Amrane ◽  
...  
Keyword(s):  
Reactive Oxygen Species ◽  
Magnetron Sputtering ◽  
Visible Light ◽  
Metallic Nanoparticles ◽  
Reaction Rate ◽  
Potassium Dichromate ◽  
Reactive Oxygen ◽  
Oh Radicals ◽  
Primary Role ◽  
Oxygen Species

In the present study, we propose a new photocatalytic interface prepared by high-power impulse magnetron sputtering (HiPIMS), and investigated for the degradation of Reactive Green 12 (RG12) as target contaminant under visible light light-emitting diodes (LEDs) illumination. The CuxO/TiO2 nanoparticulate photocatalyst was sequentially sputtered on polyester (PES). The photocatalyst formulation was optimized by investigating the effect of different parameters such as the sputtering time of CuxO, the applied current, and the deposition mode (direct current magnetron sputtering, DCMS or HiPIMS). The results showed that the fastest RG12 degradation was obtained on CuxO/TiO2 sample prepared at 40 A in HiPIMS mode. The better discoloration efficiency of 53.4% within 360 min was found in 4 mg/L of RG12 initial concentration and 0.05% Cuwt/PESwt as determined by X-ray fluorescence. All the prepared samples contained a TiO2 under-layer with 0.02% Tiwt/PESwt. By transmission electron microscopy (TEM), both layers were seen uniformly distributed on the PES fibers. The effect of the surface area to volume (dye volume) ratio (SA/V) on the photocatalytic efficiency was also investigated for the discoloration of 4 mg/L RG12. The effect of the presence of different chemicals (scavengers, oxidant or mineral pollution or salts) in the photocatalytic medium was studied. The optimization of the amount of added hydrogen peroxide (H2O2) and potassium persulfate (K2S2O8) was also investigated in detail. Both, H2O2 and K2S2O8 drastically affected the discoloration efficiency up to 7 and 6 times in reaction rate constants, respectively. Nevertheless, the presence of Cu (metallic nanoparticles) and NaCl salt inhibited the reaction rate of RG12 discoloration by about 4 and 2 times, respectively. Moreover, the systematic study of reactive oxygen species’ (ROS) contribution was also explored with the help of iso-propanol, methanol, and potassium dichromate as •OH radicals, holes (h+), and superoxide ion-scavengers, respectively. Scavenging results showed that O2− played a primary role in RG12 removal; however, •OH radicals’ and photo-generated holes’ (h+) contributions were minimal. The CuxO/TiO2 photocatalyst was found to have a good reusability and stability up to 21 cycles. Ions’ release was quantified by means of inductively coupled plasma mass spectrometry (ICP-MS) showing low Cu-ions’ release.

scholarly journals Hydrogenation Properties of LnAl2 (Ln = La, Eu, Yb), LaGa2, LaSi2 and the Crystal Structure of LaGa2H0.71(2)

Crystals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 193 ◽  
Author(s):  
Anton Werwein ◽  
Christopher Benndorf ◽  
Marko Bertmer ◽  
Alexandra Franz ◽  
Oliver Oeckler ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Hydrogen Gas ◽  
Hydrogen Atoms ◽  
Zintl Phases ◽  
Trigonal Bipyramidal ◽  
Transmission Electron ◽  
Hydrogenation Reactions ◽  
Lanthanide Metals

Many Zintl phases take up hydrogen and form hydrides. Hydrogen atoms occupy interstitial sites formed by alkali or alkaline earth metals and / or bind covalently to the polyanions. The latter is the case for polyanionic hydrides like SrTr2H2 (Tr = Al, Ga) with slightly puckered honeycomb-like polyanions decorated with hydrogen atoms. This study addresses the hydrogenation behavior of LnTr2, where the lanthanide metals Ln introduce one additional valence electron. Hydrogenation reactions were performed in autoclaves and followed by thermal analysis up to 5.0 MPa hydrogen gas pressure. Products were analyzed by powder X-ray and neutron diffraction, transmission electron microscopy, and NMR spectroscopy. Phases LnAl2 (Ln = La, Eu, Yb) decompose into binary hydrides and aluminium-rich intermetallics upon hydrogenation, while LaGa2 forms a ternary hydride LaGa2H0.71(2). Hydrogen atoms are statistically distributed over two kinds of trigonal-bipyramidal La3Ga2 interstitials with 67% and 4% occupancy, respectively. Ga-H distances (2.4992(2) Å) are considerably longer than in polyanionic hydrides and not indicative of covalent bonding. 2H solid-state NMR spectroscopy and theoretical calculations on Density Functional Theory (DFT) level confirm that LaGa2H0.7 is a typical interstitial metallic hydride.

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