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CeO promoted with either 1 wt% Pt or 1 wt% Pd was evaluated as a model system for passive NO adsorber applications. According to NO storage experiments conducted over the temperature range 80-160 °C, promotion with Pt resulted in higher NO storage efficiencies than for the Pd-promoted material. However, for NO storage at 80 and 120 °C, the latter released more NO below 350 °C during temperature-programmed desorption in relative and absolute terms, the Pt analog releasing most of its stored NO above 350 °C. DRIFT spectra showed that the use of Pd leads to preferential adsorption of NO in the form of nitrites, while predominately nitrate formation is observed over the Pt promoted material. Overall, the use of Pd promoted CeO is preferred for low temperature NO storage and release due to its ability to store NO as thermally labile nitrites. Graphical Abstract: [ABSTRACT FROM AUTHOR]

NO oxidation was studied over Pt/CeO2 and Pt/SiO2 catalysts. Apparent activation energies ( E a) of 31.4 and 40.6 kJ/mole were determined for Pt/CeO2 and Pt/SiO2, respectively, while reaction orders for NO and O2 were fractional and positive for both catalysts. Pre-treatment of the catalysts with SO2 caused a decrease in the E a values, while the reaction orders were only slightly changed. In situ DRIFTS measurements indicated that high concentrations of nitrate species were formed on the surface of Pt/CeO2 during NO oxidation, while almost no surface species could be detected on Pt/SiO2. The addition of SO2 resulted in the formation of a highly stable sulfate at the expense of nitrate species and caused an irreversible loss of catalytic activity for Pt/CeO2. [ABSTRACT FROM AUTHOR]

Inexpensive Ni-based catalysts can afford comparable performance to costly precious metal formulations in the conversion of fat, oil, or greases (FOG) to fuel-like hydrocarbons via decarboxylation/decarbonylation (deCOx). While the addition of certain metals has been observed to promote Ni-based deCOx catalysts, the steady-state performance of bimetallic formulations must be ascertained using industrially relevant feeds and reaction conditions in order to make meaningful comparisons. In the present work, used cooking oil (UCO) was upgraded to renewable diesel via deCOx over Ni/Al2O3 promoted with Cu, Fe, or Pt in a fixed-bed reactor at 375 °C using a weight hourly space velocity (WHSV) of 1 h−1. Although all catalysts fully deoxygenated the feed to hydrocarbons throughout the entire 76 h duration of these experiments, the cracking activity (and the evolution thereof) was distinct for each formulation. Indeed, that of the Ni-Cu catalyst was low and relatively stable, that of the Ni-Fe formulation was initially high but progressively dropped to become negligible, and that of the Ni-Pt catalyst started as moderate, varied considerably, and finished high. Analysis of the spent catalysts suggests that the evolution of the cracking activity can be mainly ascribed to changes in the composition of the metal particles. [ABSTRACT FROM AUTHOR]

Pt represents an effective promoter of supported Ni catalysts in the transformation of tristearin to green diesel via decarbonylation/decarboxylation (deCOx), conversion increasing from 2% over 20% Ni/Al2O3 to 100% over 20% Ni-0.5% Pt/Al2O3 at 260 °C. Catalyst characterization reveals that the superior activity of Ni-Pt relative to Ni-only catalysts is not a result of Ni particle size effects or surface area differences, but rather stems from several other phenomena, including the improved reducibility of NiO when Pt is present. Indeed, the addition of a small amount of Pt to the supported Ni catalyst dramatically increases the amount of reduced surface metal sites, which are believed to be the active sites for deCOx reactions. Further, Pt addition curbs the adsorption of CO on the catalyst surface, which decreases catalyst poisoning by any CO evolved via decarbonylation, making additional active sites available for deoxygenation reactions and/or preventing catalyst coking. Specifically, Pt addition weakens the Ni-CO bond, lowering the binding strength of CO on surface Ni sites. Finally, analysis of the spent catalysts recovered from deCOx experiments confirms that the beneficial effect of Pt on catalyst performance can be partially explained by decreased coking and fouling. [ABSTRACT FROM AUTHOR]

Abstract: A dual catalyst system for the Selective Catalytic Reduction of NO x with hydrocarbons (HC-SCR), including distinct low and high temperature formulations, is proposed as a means to abate NO x emissions from diesel engines. Given that satisfactory high temperature HC-SCR catalysts are already available, this work focuses on the development of an improved low temperature formulation. Pt supported on multiwalled carbon nantubes (MWCNTs) was found to exhibit superior NO x reduction activity in comparison with Pt/Al2O3, while the MWCNT support displayed a higher resistance to oxidation than activated carbon. Refluxing the MWCNT support in a 1:1 mixture of H2SO4 and HNO3 prior to the metal deposition step proved to be beneficial for the metal dispersion and the NO x reduction performance of the resulting catalysts. This support effect is ascribed to the increased Brønsted acidity of the acid-treated MWCNTs, which in turn enhances the partial oxidation of the hydrocarbon reductant. Further improvements in the HC-SCR performance of MWCNT-based formulations were achieved using a 3:1 Pt–Rh alloy as the supported phase. [ABSTRACT FROM AUTHOR]

The storage and reduction of NO x was examined over a series of mechanically mixed LaMn 0.9 Fe 0.1 O 3 (LMF) + Ba/Al 2 O 3 (BA), Pt-LMF + BA and LMF + BA + Pt/Al 2 O 3 (PA) catalysts in order to investigate the function of Pt in plasma-assisted NSR reaction. Efforts were also made to optimize the location of Pt to give the best H 2 reduction ability. [ABSTRACT FROM AUTHOR]

Pt- and Pd-promoted CexZr1-xO2 mixed oxides were characterized and investigated for passive NOx adsorber applications. X-ray diffraction analysis revealed a phase transition from tetragonal to cubic with increasing cerium content in CexZr1-xO2, while H2 and CO chemisorption data in all cases indicated average Pt and Pd particle sizes of close to 2 nm. H2-temperature programmed reduction (TPD) measurements revealed a shift of the Pt reduction peak to higher temperature with increasing Ce content, consistent with a corresponding increase in the degree of Pt oxidation. According to microreactor data, doping Ce into the ZrO2 lattice resulted in a significant improvement in low temperature (80-160 °C) NOx storage efficiency. Diffuse reflectance infrared Fourier transform spectroscopy measurements on Pt/CexZr1-xO2 showed that as Ce content increased, relatively more nitrite species were generated during NOx storage. However, oxidation of nitrite to nitrate during subsequent NOx-TPD increasing the concentration of more thermally stable nitrate also correlated with increased Ce content. The use of Pd as a promoter resulted in decreased NOx storage efficiency compared to Pt, although low-temperature NOx desorption behavior was improved. This is attributed to decreased formation of nitrate during NOx storage compared to that of Pt, as well as the lower activity of Pd for oxidation of nitrite to nitrate during subsequent NOx-TPD. To achieve more balanced NOx storage and desorption behavior, Ce0.2Zr0.8O2 was promoted with both Pt and Pd, resulting in superior overall NOx performance relative to its Pt and Pd analogues. After hydrothermal aging at 750 °C for 16 h, the copromoted sample still maintained excellent NOx adsorption-desorption performance. [ABSTRACT FROM AUTHOR]

Model Pt/Ce 0.9 Pr 0.1 O 2 and Pt/CeO 2 NO x storage–reduction catalysts were prepared via nitrate calcination, co-precipitation and carbon-templating routes. Raman spectroscopic data obtained on the catalysts indicated that the introduction of praseodymium into the ceria lattice increased the concentration of defect sites (vacancies), arising from the higher reducibility of the Pr 4+ cation compared to Ce 4+ . For the Pr-promoted samples, H 2 -TPR profiles contained high temperature bulk reduction peaks which were less pronounced compared with their ceria analogs, indicating that the presence of praseodymium enhances oxygen mobility due to the creation of lattice defects. Under lean-rich cycling conditions, the cycle-averaged NO x conversion of the Pt/Ce 0.9 Pr 0.1 O 2 samples was in each case substantially higher than that of the Pt/CeO 2 analog, amounting to a difference of 10–15% in the absolute NO x conversion in some cases. According to DRIFTS data, a double role can be assigned to Pr doping; on the one hand, Pr accelerates the oxidation of adsorbed NO x species during the lean periods. On the other hand, Pr doping destabilizes the adsorbed NO x species during the rich periods, and the kinetics of nitrate decomposition are faster on Pt/Ce 0.9 Pr 0.1 O 2 , leading to improved catalyst regeneration. These results suggest that ceria-based mixed oxides incorporating Pr are promising materials for NO x storage–reduction catalysts intended for low temperature operation. [ABSTRACT FROM AUTHOR]

Abstract: The liquid phase upgrading of a model bio-oil was studied over a series of supported Pt catalysts. Pt/Al2O3 showed the highest activity for deoxygenation, the oxygen content of the model oil decreasing from an initial value of 41.4wt% to 2.8wt% after upgrading. GC–MS analysis of the oil showed it to be highly aromatic, the major components corresponding to alkyl-substituted benzenes and cyclohexanes. CO2 was formed as the major gaseous product, together with lower yields of H2 and C1–C6 hydrocarbons. Based on the product distribution, a reaction scheme is proposed in which light oxygenates predominantly undergo reforming to CO2 and H2, with C–O bond breaking/hydrogenation (to afford alkanes) as a minor pathway. In a parallel process, aromatics undergo C–O cleavage/hydrogenation, affording benzenes and cyclohexanes. The highly alkylated nature of the products appears to be a consequence of the acidic nature of the reaction medium, favoring the occurrence of aromatic electrophilic substitution reactions. [Copyright &y& Elsevier]