Reduction and oxidation of a Pd/activated carbon catalyst: evaluation of effects

Abstract

A commercial Pd/activated carbon catalyst (10%) was treated using several redox processes: reduction with gaseous hydrogen at 140°C, reduction by negative electrochemical polarization in acidic and basic environments, oxidation with aqueous hydrogen peroxide, and positive electrochemical polarization in acidic and basic environments. To establish the electrochemical reduction/oxidation conditions, the potentials of hydrogen and oxygen evolution at Pd/AC powder electrodes were determined from cyclic voltammetric (CV) measurements. The samples were examined for the presence of palladium oxide phases on dispersed metal particles using XRD, TPR, and TPD. The metal oxide phase disappeared following hydrogen and electrochemical reduction. Oxidative treatment of the commercial catalyst differentiated the palladium oxide layers on the metal particle surface. Changes in the surface chemistry of the Pd/PdO/AC system were confirmed by the electrochemical behavior of electrodes prepared from the carbon samples.

Continuous Hydrogenation of Aqueous Furfural Using a Metal-Supported Activated Carbon Monolith

“…All Pd catalysts showed a negative peak between 45 and 75 °C (Figure SI3B). These peaks are indicative of PdHx (Pd hydride) decomposition due to freely available PdO and have been reported for Pd-supported catalysts in the range from 60 to 80 °C. − The ACM support (without Pd) did show a negative peak as well at 48 °C, which we attribute to an unknown off-gas component potentially due to the binder.…”

“…The positive peak at 75 °C is indicative of further PdO reduction and has been reported on activated carbon and Al 2 O 3 supports. 22,23,26 Similar to Pd/ ACM analysis, we attribute the peaks at 350 and 560 °C to hydrogen's reaction with oxygen functional groups on the carbon surface or a gasification reaction with the carbon.…”

“…21 Some Pd on activated carbon materials only show the low-temperature negative peak (50−80 °C) with the associated H 2 consumption peak (75−100 °C), which has been suggested to be due to a weak interaction of PdO with carbon. 22,23 These differences may be attributed to different metal support interactions in ACM from the other two catalysts since the ACM support is manufactured from activated carbon, binders, and other additives. Scanning electron microscopy− energy-dispersive X-ray spectroscopy (SEM−EDS) analysis indicates some co-location of Pd with Al and Si, suggesting interaction with a ceramic binder, but much of the Pd appears to be distributed on carbon (Figure S4).…”

A Heterogeneous Catalyst for the Transformation of Fatty Acids to α-Olefins

“…The effect of phosphine on the catalytic performance was tested in decarbonylative dehydration reactions involving 1 mol % Pd and stearic acid 1a as a model fatty acid substrate activated by stoichiometric amounts of acetic anhydride (Ac 2 O), which adds oxidatively as a mixed anhydride to the metal center (Table 1). 14,18 First, as shown in entry 1, in which only the starting materials were recovered, the Pd/C catalyst was inactive in the absence of phosphine, even after pre-reduction 38 with gaseous hydrogen at 140 °C. Moreover, the nature of the phosphine ligands, depicted in Figure 1, strongly influences both the activity and the selectivity (entries 2−10), with the chelating phosphines DPEphos and Xantphos giving excellent selectivity (>95%) and good yields (entries 7 and 8, respectively; 10 mol % ligand).…”

Cyclovoltammetric studies of carbon materials-supported palladium

“…The double cathodic peak present on the CVs of activated carbon-supported palladium systems indicates the presence of various forms of palladium oxides on the activated Fig. 8 Cyclic voltammograms of activated carbon based electrodes at rising anodic reverse potentials carbon surface [34,35]. Palladium electro-oxidation does not affect the oxidation or reduction of hydrogen during cathodic polarization for AC (see Figs.…”