TY - JOUR
T1 - Novel one step preparation of silica supported Pd/Sr and Pd/Ba catalysts via an organometallic precursor
T2 - Application in hydrodechlorination and hydrogenation
AU - Ding, Errun
AU - Jujjuri, Satyakrishna
AU - Sturgeon, Matthew
AU - Shore, Sheldon G.
AU - Keane, Mark A.
PY - 2008/10/15
Y1 - 2008/10/15
N2 - A gas phase hydrodechlorination (HDC) of chlorobenzene (CB) and 1,2-dichlorobenzene (1,2-DCB) has been examined over Pd/SiO2 (prepared by impregnation with Pd(C2H3O2)2) and two alkaline earth metal (AEM = Sr and Ba) promoted Pd/SiO2 catalysts prepared from the organometallic precursor {(DMF)xAEMPd(CN)4}8 (AEM = Sr, Ba; x = 4, 3). While Sr/SiO2 or Ba/SiO2 exhibited no measurable HDC activity, the bimetallic catalysts delivered specific HDC rates (per Pd metal surface area) that were up to a factor of 20 times higher than that recorded for Pd/SiO2. The initial fractional dechlorination recorded for Sr-Pd/SiO2 and Ba-Pd/SiO2 was up to two orders of magnitude greater than that for Pd/SiO2. We associate this promotional effect with a surface Pd/AEM synergy that enhances Pd dispersion with a resultant increase in H2 chemisorption capacity allied to a more effective C-Cl bond activation for hydrogen scission. Bulk and surface catalyst characteristics, pre-and post-reaction, have been probed by IR, BET, TPR, H2 chemisorption/TPD, XRD, XPS and TEM-EDX analyses. While 1,2-DCB conversion over Pd/SiO2 was lower than that observed for CB due to inhibitory inductive and steric effects, CB and DCB reactivity were comparable over AEM-Pd/SiO2. Each catalyst exhibited a temporal decline in HDC performance that we link to deleterious Cl interactions which impact H2 uptake/release capacity. Although the bimetallic catalysts were less susceptible to deactivation, the samples post-HDC retain an appreciable Cl content with a redispersion of both AEM and Pd components and a disruption to the surface electronic characteristics that is apparent from the XPS profiles. The presence of AEM had no effect on benzene hydrogenation performance over freshly activated samples but post-HDC, Pd/SiO2 exhibited depleted hydrogenation activity whereas both bimetallics (notably Sr-Pd/SiO2) generated a significantly enhanced hydrogenation response that we ascribe to a surface restructuring that is beneficial for aromatic reduction. © 2008 Elsevier B.V. All rights reserved.
AB - A gas phase hydrodechlorination (HDC) of chlorobenzene (CB) and 1,2-dichlorobenzene (1,2-DCB) has been examined over Pd/SiO2 (prepared by impregnation with Pd(C2H3O2)2) and two alkaline earth metal (AEM = Sr and Ba) promoted Pd/SiO2 catalysts prepared from the organometallic precursor {(DMF)xAEMPd(CN)4}8 (AEM = Sr, Ba; x = 4, 3). While Sr/SiO2 or Ba/SiO2 exhibited no measurable HDC activity, the bimetallic catalysts delivered specific HDC rates (per Pd metal surface area) that were up to a factor of 20 times higher than that recorded for Pd/SiO2. The initial fractional dechlorination recorded for Sr-Pd/SiO2 and Ba-Pd/SiO2 was up to two orders of magnitude greater than that for Pd/SiO2. We associate this promotional effect with a surface Pd/AEM synergy that enhances Pd dispersion with a resultant increase in H2 chemisorption capacity allied to a more effective C-Cl bond activation for hydrogen scission. Bulk and surface catalyst characteristics, pre-and post-reaction, have been probed by IR, BET, TPR, H2 chemisorption/TPD, XRD, XPS and TEM-EDX analyses. While 1,2-DCB conversion over Pd/SiO2 was lower than that observed for CB due to inhibitory inductive and steric effects, CB and DCB reactivity were comparable over AEM-Pd/SiO2. Each catalyst exhibited a temporal decline in HDC performance that we link to deleterious Cl interactions which impact H2 uptake/release capacity. Although the bimetallic catalysts were less susceptible to deactivation, the samples post-HDC retain an appreciable Cl content with a redispersion of both AEM and Pd components and a disruption to the surface electronic characteristics that is apparent from the XPS profiles. The presence of AEM had no effect on benzene hydrogenation performance over freshly activated samples but post-HDC, Pd/SiO2 exhibited depleted hydrogenation activity whereas both bimetallics (notably Sr-Pd/SiO2) generated a significantly enhanced hydrogenation response that we ascribe to a surface restructuring that is beneficial for aromatic reduction. © 2008 Elsevier B.V. All rights reserved.
KW - Ba-Pd/SiO 2
KW - Benzene hydrogenation
KW - Chlorobenzene(s) hydrodechlorination
KW - Electronic effects
KW - Pd/SiO 2
KW - Sr-Pd/SiO 2
KW - Surface reconstruction
UR - http://www.scopus.com/inward/record.url?scp=53349168933&partnerID=8YFLogxK
U2 - 10.1016/j.molcata.2008.07.020
DO - 10.1016/j.molcata.2008.07.020
M3 - Article
VL - 294
SP - 51
EP - 60
JO - Journal of Molecular Catalysis A: Chemical
JF - Journal of Molecular Catalysis A: Chemical
SN - 1381-1169
IS - 1-2
ER -