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  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/48—After-treatment of electroplated surfaces
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  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
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  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
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  • B01J35/615—100-500 m2/g
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  • B01J35/617—500-1000 m2/g
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  • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
  • B01J35/63—Pore volume
  • B01J35/633—Pore volume less than 0.5 ml/g
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  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
  • B01J35/64—Pore diameter
  • B01J35/647—2-50 nm
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
  • B01J37/0018—Addition of a binding agent or of material, later completely removed among others as result of heat treatment, leaching or washing,(e.g. forming of pores; protective layer, desintegrating by heat)
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/0201—Impregnation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/0215—Coating
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
  • B01J37/341—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation
  • B01J37/343—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation of ultrasonic wave energy
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
  • B01J37/348—Electrochemical processes, e.g. electrochemical deposition or anodisation
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  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
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  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
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  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/48—After-treatment of electroplated surfaces
  • C25D5/50—After-treatment of electroplated surfaces by heat-treatment
  • C25D5/505—After-treatment of electroplated surfaces by heat-treatment of electroplated tin coatings, e.g. by melting
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  • C25D7/00—Electroplating characterised by the article coated
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  • B01J2235/00—Indexing scheme associated with group B01J35/00, related to the analysis techniques used to determine the catalysts form or properties
  • B01J2235/05—Nuclear magnetic resonance [NMR]
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  • B01J2235/00—Indexing scheme associated with group B01J35/00, related to the analysis techniques used to determine the catalysts form or properties
  • B01J2235/10—Infrared [IR]
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  • B01J2235/00—Indexing scheme associated with group B01J35/00, related to the analysis techniques used to determine the catalysts form or properties
  • B01J2235/15—X-ray diffraction
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  • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties

Definitions

• Oxide supports such as silica or alumina are important components of heterogeneous catalysts used in petroleum refining, in automotive exhaust catalytic converters, and in the pharmaceutical industry, to name just a few examples.
• oxide supports designed for gas-phase reactions are not suitable for aqueous-phase reactions at these elevated temperatures as they are susceptible to degradation in the aqueous phase at elevated temperatures.
• alumina undergoes a phase change from ⁇ - ⁇ 1 2 0 3 to boehmite at 473 K with a consequent loss of surface area.
• mesoporous silica SBA-15 suffers from collapse of the well-ordered mesoporous structure when heated to 473 K in liquid water, resulting in loss of its surface area and structural integrity. Accordingly there is a need for oxide supports and catalysts that are able to maintain structural integrity and catalytic activity under harsh treatment conditions.
• the present disclosure provides catalyst support materials that are coated with a thin carbon over-layer and methods for making the same.
• a supporting oxide material which may or may not have a catalytic material already deposited on the surface, is coated with a thin carbon layer.
• the supporting material and carbon layer are then subjected to partial pyrolysis, resulting in a stable material that is able to withstand high temperatures under aqueous phase conditions.
• the catalyst support may or may not have a catalyst material deposited on the thin carbon layer.
• the support may be reusable, allowing for the repeated deposition and removal of the thin carbon layer.
• FIG. 1 is a flowchart showing a method for forming a catalyst support according to a first embodiment of the present disclosure.
• FIG. 2 is a flowchart showing a method for forming a catalyst support according to another embodiment of the present disclosure.
• FIG. 3 is a flowchart showing a method for forming a catalyst support according to a further embodiment of the present disclosure.
• FIG. 4 is a flowchart showing a method for forming a catalyst support according to a still further embodiment of the present disclosure.
• FIG. 5 is a schematic illustration of a method or reusing and reapplying the supporting material and thin carbon coating according to an embodiment of the present disclosure.
• FIG. 6 is a schematic illustration of a method or reusing and reapplying the supporting material and thin carbon coating according to an embodiment of the present disclosure.
• Fig. 7 is an HRTEM image of calcined SBA-15.
• Fig. 8 is an elemental carbon map of SBA-15.
• Fig. 9 is an HRTEM image of 10 wt carbon-SBA-15.
• Fig. 10 is an elemental carbon map of 10 wt carbon-SBA-15.
• Fig. 11 is an N 2 sorption isotherm obtained from calcined SBA-15 (circles) and 10 wt carbon-SBA-15 (squares).
• Fig. 12 shows the pore size distribution for calcined SBA-15 (circles) and 10 wt carbon-SBA-15 (squares).
• Fig. 13 is a STEM image of calcined SBA-15, the inset shows well-ordered pores.
• Fig. 14 is a STEM image of calcined SBA-15 after treatment in liquid water at 473 K for
• Fig. 15 is a STEM image of 10 wt % carbon-SBA-15, the inset shows well-ordered pores.
• Fig. 16 is a STEM image of 10 wt % carbon-SBA-15 after treatment in liquid water at 473 K for 12 hours.
• Fig. 17 is an HAADF-STEM image of 25 wt% carbon-SBA-15.
• Fig. 18 is an HAADF-STEM image of 25 wt% carbon-SBA-15 after treatment in liquid water at 473 K for 12 hours.
• Fig. 19 is a STEM image of silica gel.
• Fig. 20 is a STEM image of silica gel after treatment in liquid water at 473 K for 12 hours.
• Fig. 21 is a STEM image of 10 wt carbon-silica gel.
• Fig. 22 is a STEM image of 10 wt carbon-silica gel after treatment in liquid water at 473 K for 12 hours.
• Fig. 23 is a STEM image of fumed alumina.
• Fig. 24 is a STEM image of fumed alumina after treatment in liquid water at 473 K for 12 hours.
• Fig. 25 is a STEM image of 10 wt % carbon- alumina.
• Fig. 26 is a STEM image of 10 wt % carbon- alumina after treatment in liquid water at 473 K for 12 hours.
• Fig. 28 is a structural model reproducing the experimental spectra.
• Fig. 29 is an HRSEM image of Stober spheres.
• Fig. 30 is an HRSEM image of Stober spheres after treatment in liquid water at 473 K for 12 hr
• Fig. 31 is an HRSEM image of 10 wt carbon-Stober spheres.
• Fig. 32 is an HRSEM image of 10 wt carbon-Stober spheres after treatment in liquid water at 473 K for 12 hr
• Fig. 33 is FTIR spectra of calcined a) SBA-15, b) 10 wt% carbon-SBA-15, and after rehydration at room temperature, (c) 10 wt carbon-SBA-15 and (d) SBA-15.
• Fig. 34 is a graph showing XRD patterns of fumed alumina (a) and 10 wt carbon- alumina (b), and of 10 wt carbon-alumina (c) and fumed alumina (d) after treatment in liquid water at 473 K for 12 h.
• Fig. 35 is HAADF-STEM images of 1 to 1.5 nm Pd nanoparticles (0.5 wt ) supported on silica gel (a) and on 10 wt carbon-silica gel (b).
• Fig. 36 is a graph showing selective hydrogenation of a mixture of acetylene/ethylene (1:70) on 0.5 wt Pd on alumina (open circles) and on 10 wt carbon-alumina (closed circles); 0.5 wt Pd on silica gel (open squares) and on 10 wt carbon-silica gel (closed squares).
• Fii I. 37 is a TGA of sucrose-containng SBA-15 performed under N 2 flow from 25-800°C
• Fii ⁇ . 38 is an image of 0.5 wt % Pd on silica.
• Fii I. 39 is a close-up image of the 0.5 wt % Pd on silica of Fig. 38.
• Fii ⁇ . 40 shows the 0.5 wt % Pd on silica after treatment in liquid water at 473 K for 12 hr.
• Fii l. Al is a close-up image of the 0.5 wt % Pd on silica of Fig. 40.
• Fii I- 2 is an image of 0.5 wt % Pd on carbon-silica.
• Fii I. 43 is a close-up image of the 0.5 wt % Pd on carbon-silica of Fig. 42.
• Fii >. 44 shows the 0.5 wt % Pd on carbon-silica after treatment in liquid water at 473 K for 12 hr.
• Fii I. 45 is a close-up image of the 0.5 wt % Pd on carbon-silica of Fig. 44.
• Fii ⁇ . 46 is an image of Carbon on 0.5 wt % Pd/silica.
• Fii I- 7 is a close-up image of the Carbon on 0.5 wt % Pd/silica of Fig. 46.
• Fii ⁇ . 48 shows the Carbon on 0.5 wt % Pd/silica after treatment in liquid water at 473 K for 12 hr.
• Fii ⁇ . 49 is a close-up image of the Carbon on 0.5 wt % Pd/silica of Fig. 48.
• the present disclosure provides catalyst support materials that are coated with a thin carbon over-layer and methods for making the same.
• the thin carbon over-layer results in a more stable material and, surprisingly, when combined with the carbon coated supports of the present disclosure, some catalytic materials demonstrate higher catalytic activity than the same catalysts deposited on uncoated supports.
• Fig. 1 is a flow chart showing a general embodiment of the presently described method.
• a catalyst support material, or precursor therefore, is exposed to an aqueous solution containing a carbon precursor.
• the aqueous solution is then allowed to evaporate, typically while stirring, until a dry product is produced.
• the dry product is then partially pyrolyzed to produce a catalyst support with a thin carbon over-layer.
• the active phase can then be deposited on this carbon-coated surface just like on any carbon support used to make catalysts.
• this surface carbon is an active form of carbon, with functional groups and anchoring sites created uniquely through a combination of using a suitable precursor and the appropriate pyrolysis conditions.
• the catalyst support may be any suitable material including, for example, oxide supports such as silica, SBA-15, alumina, niobia, and ceria.
• the catalyst support may be exposed to the aqueous solution in a precursor form, and thus synthesized in vitro, or already synthesized.
• the catalyst support may be a fully formed (granulated) commercially available support or in powder form, for example Sigma-Aldrich Davisil silica gel.
• the support may be a mixed-oxide such as aluminosilicate, or a composite such as a metal oxide on carbon.
• catalyst support material of any size or structure and having or incorporating any shape.
• One of the primary functions of many catalyst supports is to provide a high surface area.
• One way in which this is achieved is by preparing catalyst supports comprised of nanosized primary particles.
• Metal (or other) catalysts are frequently deposited on such oxides because the nanosized primary particles constitute the porous structure of the support, thereby creating a catalyst support with a high surface area.
• Another class of catalyst support has an ordered structure with a one- , two- or three- dimensional arrangement of pores. These pores can have a cylindrical shape or a complex internal geometry and interconnections.
• the surface area accessible to the catalytic material includes the internal surfaces, which are concave. The methods describe herein easily coat both convex and concave surfaces, as well as regular, and irregular surfaces, and combinations thereof.
• the carbon precursor may be sucrose.
• suitable carbon precursors may be glucose, fructose, maltose, lactose, starch, and cellulose.
• concentration of sucrose (or other carbon precursor) in the aqueous solution determines the thickness of the resulting carbon layer.
• aqueous solutions of between 5 and 30 wt sucrose will produce coatings with desirable attributes.
• an aqueous sucrose solution according to the present disclosure may be between 5 and 30 wt , 5 and 25 wt , 7 and 20 wt , 10 and 20 wt , or any other suitable wt .
• 10 wt and 25 wt sucrose solutions resulted in catalysts that, when compared to the equivalent uncoated supports, have increased stability and, in some cases, increased catalytic activity.
• the aqueous solution containing the catalyst support material and carbon precursor is allowed to evaporate, typically under stirring to prevent settling.
• the solution may be shaken, turned, rotated, or otherwise disturbed so as to prevent settling. This may be performed at room temperature or at temperatures up to 80 °C to reduce the evaporation process time.
• the temperature and length of time at which the dried material is subjected to pyrolysis will largely depend on the actual material being used. For the purpose of the present disclosure, complete pyrolysis is considered to have been achieved when 100% of the carbon materials is graphitic carbon (i.e., above 800 °C) with no remaining functional groups.
• Partial pyrolysis is achieved when at least 25% of the carbon materials contains functional groups (i.e., 400 °C). Accordingly, the methods of the present disclosure use partial pyrolysis to ensure that the catalyst material coated with carbon retains some functional groups (partially hydrophilic) needed for anchoring of metal nanoparticles or other active phases. In turn, graphitic carbon is inert and hydrophobic and typically needs to be surface-functionalized before anchoring metal nanoparticles or other active phases.
• pyrolysis may be performed for between 1 and 8 hours, between 1 and 6 hours, between 1 and 4 hours, or around 2 hours at a temperature of between 200 °C and 600 °C, between 300 °C and 500 °C, between 350 °C and 450 °C, or around 400 °C.
• catalytic materials may be deposited on the support materials prior to coating.
• material that may be deposited on the support material include platinum and platinum group metals (PGM) and alloys thereof, oxides, carbides, nitrides, functional materials, and other transition metals.
• PGM platinum and platinum group metals
• the catalytic material may, for example, take the form of nanoparticles.
• the particles may be monodisperse or polydisperse. In some cases the carbon layer may coat the particles entirely, in other cases a portion of the particles may be uncoated.
• Fig. 3 provides yet another embodiment, wherein additional precursors such as catalyst precursors like palladium nitrate or niobium oxalate, are added to the aqueous solution.
• additional precursors such as catalyst precursors like palladium nitrate or niobium oxalate
• the catalyst precursor is added to the aqueous solution containing the sucrose and support material. Partial pyrolysis results in both the formation of the carbon layer and the transformation of the catalyst precursors to form the active catalyst.
• the carbon layer may coat the active phase entirely (referred to herein as an "overlay er"), in other cases a portion of the active phase may be uncoated. This coating procedure improves the stability of the active phase.
• Fig. 4 provides still another embodiment showing the deposition of catalyst or other material on the surface of the coated catalyst support. If a catalyst was deposited prior to coating, the material deposited after coating may be the same or a different material from the catalyst that was previously deposited. Examples of material that may be embedded in or deposited on the carbon layer include palladium and palladium group metals and alloys thereof, oxides, carbides, functional materials, and other transition metals.
• the catalytic material may, for example, take the form of particles. The particles may be monodisperse or polydisperse.
• the support may be reusable, allowing for the repeated deposition and removal of the thin carbon layer. Accordingly, as shown in Figs.
• oxide support 22 includes a thin carbon layer 20 on which are deposited catalyst particles 24. If desired, the support can be subjected to heat treatment conditions (for example through oxidation) such that the carbon layers are burned off of the support. A new thin carbon layer 20 can then be reapplied to the support. Alternatively, as shown in Fig. 6, wherein the thin carbon layer was initially an overlayer deposited over the catalyst layers, the overlayer can be removed via heat treatment and then reapplied. It should be noted that whether the carbon layer ends up forming over (as in Fig. 6) or around (as in Fig.
• the catalyst particles may depend on the thickness of the carbon layer applied and the size of the catalyst particles. Accordingly, by controlling the wt of carbon loading, one can determine the ultimate formation of the carbon layer in relationship to the catalyst particles or any other material incorporated into the support.
• a reusable support material as described above may be desirable, for example, in situations where the catalyst is poisoned and needs to be regenerated in an oxidizing environment which would cause the carbon coating to be lost and it is desirable to regenerate it in a quick and efficient matter.
• Example I Preparation and Characterization of Carbon Coated SBA-15, Silica, and Alumina
• Pluronic P123 surfactant (4.0 g) was dissolved in deionized water (30 g) while stirring at 308 K.
• 2M HC1 120 g
• TEOS tetraethyl orthosilicate
• the solution was then transferred to a Nalgene bottle and placed in a water bath at 308 K without stirring for 20 h.
• the solid product was filtered, washed with deionized water, and air-dried at room temperature.
• the dried product was calcined in air at 773 K (5 K min "1 ramp) for 12 h to remove the P123 template.
• Infrared spectra of samples were recorded on a Nicolet 7600 FTIR analyzer equipped with an attenuated total reflectance (ATR) attachment. The spectra were acquired between 400-4000 cm “1 at 4 cm “1 resolution and 128 scans. 13 C NMR spectroscopy was performed at 100 MHz on 13 C-enriched samples washed with water to remove trapped low-molar mass species, using a Bruker DSX400 spectrometer, magic-angle spinning at 14 kHz, and highpower 1 H decoupling.
• Quantitative 13 C NMR spectra were measured using direct polarization (DP) and a Hahn echo, with recycle delays of 30 s (>5 Ti), and spectra of nonprotonated carbon atoms (and mobile segments) were obtained after recoupled ⁇ C- 1 ! dipolar dephasing.
• X-ray powder diffraction (XRD) was performed using a Scintag Pad V diffractometer (Cu Ka radiation) with DataScan 4 software (MDI, Inc.) [071]
• EFTEM energy-filtered transmission electron microscopy
• HAADF-STEM images of the SBA-15-based samples show the retained hexagonal arrangement of pores (inset) after coating the pore walls of SBA-15 (Fig. 13) with carbon (Fig. 15).
• uncoated SBA-15 loses 96% of its surface area as a result of a complete collapse of the ordered mesopores, and loss of its structural integrity (Fig. 14).
• hydrothermal stability is significantly improved after coating SBA-15 with carbon, with a surface-area loss of only 55% and a partially retained ordered mesoporous structure (Figs. 16).
• Fig. 27 shows the 13 C NMR spectrum of carbon-SBA-15 produced using 13 C enriched glucose, with the corresponding spectrum of the nonprotonated carbon atoms (and mobile segments) superimposed.
• hydrothermal stability is improved after coating St5ber spheres with carbon, with retention of the individual coated spheres and no pronounced sintering or formation of large pores after hydrothermal treatment. Furthermore, there is no delamination and formation of defects, which are generally more pronounced when thin films are deposited on convex surfaces rather than on concave ones.
• the FTIR spectra of the SBA-15-based samples show a broad absorption band at around 3200-3600 cm “1 assigned to the O-H stretching vibration, and an absorption band at around 1640 cm “1 assigned to the bending vibrations of molecular water. Both the absorption bands at around 3200-3600 cm “1 and at around 1640 cm “1 are initially small for SBA-15, which is expected because FTIR was performed on SBA-15 just after calcination to remove the surfactant, thus minimizing exposure of SBA-15 to moisture. These two absorption bands slightly increased for carbon coated SBA-15 after SBA-15 was mixed with the aqueous sucrose solution followed by carbonization.
• the surface of the uncoated silica samples used in this study consists of siloxane bridges and silanol groups.
• silicate hydrolysis occurs.
• the hydrolytic cleavage of the siloxane bonds leads to a dissolution and reprecipitation of silica, resulting in loss of both high surface area and structural integrity.
• Fig. 34 shows the XRD patterns of the alumina-based samples.
• the patterns for both uncoated (a) and carbon-coated alumina (b) are characteristic of the y-Al 2 C> 3 phase.
• the XRD pattern for uncoated alumina is characteristic of boehmite (d).
• the transformation from ⁇ - ⁇ 1 2 0 3 to boehmite is due to hydration of alumina when it is subjected to liquid water at 473 K for several hours.
• carbon coated alumina remains as ⁇ - ⁇ 1 2 0 3 after hydrothermal treatment (c). This shows that we are able to modify the surface of alumina with carbon before subjecting it to hydrothermal conditions, thereby achieving improved stability.
• the extent of carbon coating, and the carbon loading can be varied to achieve different degrees of surface modification of the y-Al 2 C> 3 surface.
• a selective catalyst will convert all of the acetylene to ethylene without hydrogenating ethylene to ethane. However, as the acetylene conversion reaches 100%, all catalysts lose selectivity and start to show formation of ethane. The less-selective catalysts also hydrogenate some of the ethylene in the feed, thus leading to excess ethane. The amount of ethane formed is therefore a good measure of the selectivity of the catalyst, because selectivity at high acetylene conversion is desired. Ethane formation is presented as the ratio of moles of ethane in the effluent to moles of ethylene in the feed, which allows comparison with other feed compositions in the literature.
• the amount of ethane formed at the same acetylene conversion is higher on the silica and alumina supports and lower on the carbon-coated supports (Fig. 36), which are comparable in selectivity to Pd/Vulcan XC carbon black.
• These catalysts prevent overhydrogenation of ethylene, even at near 100% conversion of acetylene.
• Addition of promoters, such as Ag, will further improve selectivity; here we use this test reaction to show changes in the surface chemistry at the metal-oxide interface. It is clear that coating these oxides with carbon changes the surface chemistry, making the surface more hydrophobic (fewer surface hydroxyls by FTIR); the oxide- surface chemistry is reflected in the improved selectivity for the acetylene hydrogenation.
• a hydrothermally stable support is necessary for achieving stable reactivity for metal-catalyzed reactions in the aqueous phase.
• TGA plot is shown in Fig. 37.
• the curve between the horizontal lines corresponds to the pyrolysis of sucrose (% weight loss below 100°C is loss of water in the sample).
• the vertical line at 400°C corresponds to the temperature used to pyrolyze the samples.
• the steep slope between 200-500°C shows the % weight loss of sucrose during pyrolysis indicating that not all of the O and H atoms in sucrose are lost during the pyrolysis.
• the black dash-dot line in the plot corresponds to the loss of functional groups in carbon
• the red dash line corresponds to the remaining functional groups in carbon which was estimated to be 25%.
• the carbon being formed on SBA-15 therefore contains functional groups which are very important to achieve the desired properties in the carbon layer.
• the temperature at 800°C is where we define complete pyrolysis, and is the pyrolysis temperature typically used to prepared ordered mesoporous carbon in the literature where a sacrificial templating technique is used to form the ordered carbon structures before removal of the sacrificial (usually silica) template.
• Example III Comparison of Pd nanoparticle stability after hydrothermal treatment when supported on carbon-coated silica or when supported on silica followed by coating with a carbon overlayer
• Pd nanoparticles (nominal loading 0.5 wt ) were deposited on silica supports (Pd/Si, Figs. 38 and 39), carbon-coated silica supports (Pd/C-Si, Figs. 42 and 43) and silica supports, after which both the supports and the Pd nanoparticles were coated with a carbon over-layer (C/Pd-Si, Figs. 46 and 47) and then subjected to treatment in liquid water (473 K for 12 h) (Figs. 40, 41, 44, 45, 48, and 49).
• the Pd/Si sample After the high temperature water treatment (Figs. 40 and 41), the Pd/Si sample had a measured Pd loading of ⁇ 0.1 wt by EDS due to leaching of Pd from the silica support, and the remaining Pd nanoparticles were measured in the 2-20 nm size range with low Pd dispersion due to Pd sintering. In contrast, after treatment, the Pd/C-Si sample had a measured Pd loading of 0.4 wt by EDS with 2-5 nm sized Pd nanoparticles maintaining its high Pd dispersion (Figs.
• the C/Pd-Si sample had a measured Pd loading of .4 wt by EDS with 1.5-4 nm sized Pd nanoparticles and a high Pd dispersion (Figs. 48 and 49), demonstrating that the thin carbon layer, whether placed over or under the Pd nanoparticles, serves to inhibit the sintering of Pd during high temperature liquid treatment.
• the thin carbon layer inhibits the change in the structure of the silica support during high temperature liquid treatment since Pd sintering is often accompanied by (and could be caused by) a loss in the structural integrity of the silica support.

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