Catalytic wet oxidation of lactose

The catalytic wet oxidation of lactose to carbon dioxide/water and to a value-added product, lactobionic acid, has been demonstrated in a flow reactor. Lactose (milk sugar) is a low value byproduct of the dairy industry and makes up the largest part of the solids in cheese whey. Costs associated with cheese whey disposal are driving the need to develop alternative disposal methods. Pt/Al2O3, CeMn mixed-metal oxides, and Pt/CeMn catalysts have all been shown to effectively convert lactose to carbon dioxide and water at temperatures up to 443 K and pressures of 100 psig. Pt/CeMn demonstrated the lowest level of side-product formation. A BiPd/C catalyst was shown to convert essentially all lactose to lactobionic acid at similar temperature and pressure. Lactobionic acid selectivity was a strong function of oxygen concentration in the feed. The BiPd/C also produced a high yield of lactobionic acid at lower pH and higher temperatures than previously reported. © 2008 American Chemical Society

Using life cycle assessment to guide catalysis research

The use of life cycle assessment (LCA) as a tool to guide catalyst development is demonstrated by comparing the environmental impact of acrylic acid production from propylene, the current commercial feedstock, to propane as an alternate feedstock. Acrylic acid is currently produced in a two-step process from propylene. Because of its lower cost, propane is an attractive alternative to propylene; however, no catalysts are currently available that can compete with the high yield of the propylene process. The LCA was performed using SimaPro, and impact assessment was determined using the Eco-Indicator 99 method. A comparison of the two feedstocks at the 87% yield of the current commercial propylene process demonstrated that switching to propane would decrease the environmental impact of the process by 20%. Determination of environmental impact as the yield from the potential propane process was varied predicts that, at yields exceeding 6%, the propane process will have a lower environmental impact than the current propylene process. By focusing on particular categories such as fossil fuels or climate change, the propane process will have a lower impact for yields exceeding 15 and 33%, respectively. The current catalyst yield of up to 48% for the propane process exceeds these values. If reaction and waste gas heat are converted to electricity instead of steam, yields in excess of 61% will result in a lower total impact for the propane process. On the basis of raw material costs, the economic break-even point for the propane process is 59% yield. The similar yields of ~60% from propane required by economics and for a lower environmental impact represents a factor of 1.25 increase in yield over the current state-of-the-art propane catalyst compared to a factor of 1.81 increase in yield required to equal the current propylene yield. Thus, the proposed propane process may be much closer to viability than previously realized. This analysis provides an example of how LCA can compare chemical production from two different feedstocks, even if a catalyst for the reaction of interest has not been designed. The LCA analysis can also be used to determine target goals for catalysis research. © 2009 American Chemical Society

Correlation of H \u3c inf\u3e 2 heat of adsorption and ethylene hydrogenation activity for supported Re@Pd overlayer catalysts

Alumina-supported bimetallic overlayer Pd on Re (Re@Pd) catalysts were synthesized using the directed deposition technique. Hydrogen chemisorption, TEM, EDS, XRD, and ethylene hydrogenation studies were used to characterize the catalysts and provide indication of electronic modification of the Pd surface layer due to the overlayer particle structure. First principles computation and single crystal studies of Pd overlayers on Re in the literature have shown that electronic modification of the Pd overlayer is observed and leads to decreased binding strength for chemisorbed species such as H2, C2H4, and CO. Measured hydrogen chemisorption isotherms indicated that Pd was deposited on the Re and not as pure isolated Pd particles. H2 heats of adsorption, as determined by chemisorption, indicated that the Re@Pd overlayer catalysts were lower than either pure Pd or Re. The Re@Pd catalysts were slightly less active for ethylene hydrogenation than pure Pd but displayed similar apparent activation energies and H2 and C2H4 reaction orders. A linear correlation between turnover frequency and maximum heat of H2 adsorption was observed for the Pd and Re@Pd catalysts. This suggests an electronic modification of the Re@Pd catalyst surface compared to Pd as predicted in the literature by first principles computational studies. © 2009 Elsevier Inc. All rights reserved

Synthesis and characterization of supported bimetallic overlayer catalysts

The directed deposition technique was used to synthesize alumina-supported bimetallic overlayer Pd on Re (Re@Pd) and Pt on Ni (Ni@Pt) catalysts. Computational and single crystal studies have predicted unique adsorption properties for similar overlayer type catalysts compared to the monometallic catalysts. The directed deposition technique combines the use of inhibitors and a surface reaction to produce the desired overlayer structure. The Re@Pd and Ni@Pt catalysts were characterized using hydrogen chemisorption, transmission election microscopy (TEM), and energy dispersive spectroscopy (EDS) to correlate properties with synthesis conditions. H2 chemisorption indicated the proper synthesis conditions to deposit the overlayer metal on the base metal catalyst particle as desired. When a surface deposition inhibitor was not used, evidence for the formation of isolated particles of the overlayer metal was detected. Re@Pd catalysts showed decreased hydrogen heat of adsorption compared to Pd or Re monometallic catalysts as predicted by the literature. Ni@Pt catalysts demonstrated intermediate H2 heat of adsorption compared to Pt and Ni. TEM/EDS were used to demonstrate that the overlayer metal was associated with the base metal particles as desired. © 2009 Elsevier B.V. All rights reserved

Characterization of selective oxidation catalysts from polyoxometalate precursors using ammonia adsorption microcalorimetry and methanol oxidation studies

Phosphomolybdic acid (H3PMo12O40) along with niobium, pyridine and niobium/pyridine exchanged phosphomolybdic acid compounds were prepared. These compounds were converted to selective oxidation catalysts by pre-treating to 693 K in an inert atmosphere. As shown previously, the active catalyst consists of partially decomposed, partially reduced Keggin units and MoOx fragments with some MoOx fragments collected around the Nb. The amount of surface Mo species reduced to the 5+ oxidation state varied among the catalysts. Ammonia adsorption microcalorimetry and methanol oxidation studies were carried out to investigate the acid sites strength and the acid/base/redox properties of each catalyst. The addition of niobium, pyridine or both increased the ammonia heat of adsorption by 30-40 kJ/mol and the total ammonia uptake. The catalyst with both niobium and pyridine demonstrated the largest number of strong sites. For the parent H 3PMo12O40 catalyst, methanol oxidation favors the redox product (∼95% selectivity). However, catalyst deactivation occurs. The presence of niobium results in similar selectivity to redox products (∼93%) but also results in no catalyst deactivation. Incorporation of pyridine to the precursor compound, in contrast, changes the selectivity to initially favor the acid product (∼62%). Again, the catalyst deactivated and selectivity changed during deactivation to favor the redox product (∼55%). Finally, the inclusion of both niobium and pyridine results in strong selectivity to the acid product (∼95%) while also showing no catalyst deactivation and stable selectivity. Specific activity for the niobium and pyridine exchanged catalyst for the methanol oxidation reaction was twice any other catalyst. Selectivity to acid products was correlated with the amount of reduced surface Mo species. Thus, the presence of pyridine appears to enhance the acid property of the active site in the catalyst while niobium appears to stabilize the active site. © 2013 Elsevier B.V

Use of Hydrogen Chemisorption and Ethylene Hydrogenation as Predictors for Aqueous Phase Reforming of Lactose over Ni@Pt and Co@Pt Bimetallic Overlayer Catalysts

Overlayer Pt on Ni (Ni@Pt) or Co (Co@Pt) were synthesized and tested for H₂ generation from APR of lactose. H₂ chemisorption descriptor showed that Ni@Pt and Co@Pt overlayer catalysts had reduced H₂ adsorption strength compared to a Pt only catalyst, which agree with computational predictions. The overlayer catalysts also demonstrated lower activity for ethylene hydrogenation than the Pt only catalyst, which likely resulted from decreased H₂ binding strength decreasing the surface coverage of H₂. XAS results showed that overlayer catalysts exhibited higher white line intensity than the Pt catalyst, which indicates a negative d-band shift for the Pt overlayer, further providing evidence for overlayer formation. Lactose APR studies showed that lactose can be used as feedstock to produce H₂ and CO under desirable reaction conditions. The Pt active sites of Ni@Pt and Co@Pt overlayer catalysts showed significantly enhanced H₂ production selectivity and activity when compared with that of a Pt only catalyst. The single deposition overlayer with the largest d-band shift showed the highest H₂ activity. The results suggest that overlayer formation using directed deposition technique could modify the behavior of the surface metal and ultimately modify the APR activity