Temperature-programmed desoprtion of H2 from the surfaces of pd/support and Pd-Ag/support catalysts (support = Al2O3, SiO2)

Abstract

Thermal desorption of H 2 from the surface of Pd/support and Pd-Ag/support (support = Al 2 O 3 , SiO 2 ) catalysts has been investigated. Two wide desorption peaks can be observed for the 5%Pd/support catalyst. The presence of these peaks in the thermogram indicates that several adsorption states exist, which is the result of occurrance of different adsorption centers of specific bond strengths for hydrogen. The addition of silver to the palladium catalysts causes a considerable decrease in the size of the high temperature desorption peak. It is also worth noting that the temperature of the maximum of the desorption rate remains practically constant for all bimetallic catalysts studied. This means that the activation energy of the hydrogen desorption process does not change after the introduction of silver to the palladium catalyst.

Influence of the Method of Preparation of the Pd-Bi/Al2O3 Catalyst on Catalytic Properties in the Reaction of Liquid-Phase Oxidation of Glucose into Gluconic Acid

“…In contrast, both bimetallic samples showed no peak of β-PdH decomposition, which means that the presence of Bi limits the formation of this hydrogen-containing Pd phase [27,43]. Similar regularities were obtained for deposited catalysts promoted by Sn, Ag [44][45][46]. Instead, a positive peak was observed at 131-154 • C, which was observed for the samples PdBi/Al 2 O 3 and Pd→Bi/Al 2 O 3 , but without a peak of β-PdH decomposition.…”

The effect of support porosity on the selectivity of Pd–In/support catalysts in nitrate reduction

“…Those intermetallic compounds were observed for all Pd-In/support catalysts by ToF-SIMS technique independently of the In amount incorporated to the system ( Table 1). The presence of the Pd x In y phase was also confirmed by the XRD technique, but only for the system with the amount of indium higher than 2-wt% [38,39].…”

“…The accepted mechanism for the reduction of nitrates to nitrites requires promotion of the noble metal by an addition of a second metal like Cu, Ag or In [19,[30][31][32][33][34]39]. From the literature data, it also is known that some supports like TiO 2 , CeO 2 and SnO 2 in the monometallic palladium catalysts participate in the reduction of nitrates to nitrogen [8][9][10][11].…”

“…The studies that we have conducted show that palladium supported catalysts promoted with indium, after appropriate activation, are characterized by good activity and selectivity to nitrogen. For Pd-In systems supported on Al 2 O 3 and SiO 2 , strong interactions between palladium and indium leading to the formation of the intermetallic compound of In 0.52 Pd 0.48 type on the surface of carriers used [38,39] were observed. This compound was detected by XRD technique for Pd-In/support systems which contained more than 2 wt% indium.…”

“…Monometallic palladium catalysts are not very active in the reaction of nitrate reduction. However, they show high activity in the reduction of nitrites [3][4][5][12][13][14]. Among the studied bimetallic systems, palladium systems promoted with Cu, Sn, Ag or Fe supported on different kinds of oxide carriers [14][15][16][17][18][19][20], polymers [21,22], zeolites [23], active carbons [24][25][26], resin [27][28][29], showed the best catalytic characteristics.…”