Insight into Supported Metal Catalyst Stability by Quantifying Thermodynamic Interactions at the Solid-liquid Interface

Meeting Program — April 2016

 
Robert Rioux
Robert Rioux
Friedrich G. Helf­ferich Asso­ciate Pro­fes­sor of Chem­i­cal Engi­neer­ing
Penn­syl­va­nia State Uni­ver­si­ty

 
 
 
 
 
Abstract — Indus­tri­al appli­ca­tions of sup­port­ed late tran­si­tion met­al cat­a­lysts demand eco­nom­ic and scal­able syn­the­sis of these cat­a­lysts and cur­rent syn­thet­ic meth­ods lack pre­ci­sion in terms of size, shape and com­po­si­tion­al con­trol. More­over, sup­port­ed met­al cat­a­lysts suf­fer from poor sta­bil­i­ty, man­i­fest­ed in the form of sin­ter­ing (i.e., par­ti­cle growth) dur­ing reac­tion. The prop­er selec­tion of the oxide sup­port is of great impor­tance to ensure high dis­per­sion, activ­i­ty and selec­tiv­i­ty of the nanopar­ti­cles. The abil­i­ty of these sup­ports to enhance the dis­per­sion of the active met­al on their sur­face and con­trol their mor­phol­o­gy and sin­ter­ing kinet­ics is fun­da­men­tal­ly relat­ed to the nature and strength of the metal–metal oxide inter­ac­tion at the time of adsorp­tion. In this work, we have uti­lized isother­mal titra­tion calorime­try (ITC), a tech­nique capa­ble of quan­ti­fy­ing the ther­mo­dy­nam­ic descrip­tion (ΔG, ΔH, ΔS, n (sto­i­chiom­e­try)) of tran­si­tion met­al asso­ci­a­tion with a sup­port mate­r­i­al in a sin­gle exper­i­ment. After pro­vid­ing a brief intro­duc­tion to ITC and meth­ods of cat­a­lyst syn­the­sis, we will dis­cuss our results to quan­ti­fy the elec­tro­sta­t­ic inter­ac­tions between sol­vat­ed tran­si­tion met­al ions and charged ampho­teric met­al oxide sur­face. With­in this inter­ac­tion-type, we have stud­ied both refrac­to­ry and reducible met­al oxides. With a reducible met­al oxide, ceria, we demon­strate a poten­tial­ly new mech­a­nism of adsorp­tion, which may describe the suc­cess­ful sta­bi­liza­tion of noble met­als enabling main­te­nance of small sized nanopar­ti­cles com­pared to oth­er oxide sup­ports. In addi­tion to ITC, bulk uptake stud­ies have aid­ed in quan­ti­fy­ing the amount of met­al pre­cur­sor adsorbed on the sup­port sur­face and equi­lib­ri­um isotherms describe the uptake behav­ior and may pro­vide insight for pre­dict­ing long term sta­bil­i­ty of the nanopar­ti­cles. In the sec­ond half of the talk, we dis­cuss the adsorp­tion of tran­si­tion met­al oxide and hydrox­ide nanopar­ti­cles in the gal­leries of of Nb-based per­ovskites. ITC was used to quan­ti­ta­tive­ly rank the strength of adsorp­tion between the met­al nanopar­ti­cle and their propen­si­ty to sin­ter, as assessed by in-situ, high-tem­per­a­ture trans­mis­sion elec­tron microscopy. In both exam­ples, we will empha­size this ini­tial inter­ac­tion at the sol­id-liq­uid inter­face is impor­tant and con­veys a his­to­ry effect to the cat­a­lyst that is evi­dent dur­ing post-pro­cess­ing (dry­ing, cal­ci­na­tion and reduc­tion). The esti­mat­ed ther­mo­dy­nam­ic para­me­ters are expect­ed to quan­ti­fy the type of bond­ing at the inter­face, shed light on the bind­ing mech­a­nism and the growth and sin­ter­ing kinet­ics of sup­port­ed cat­a­lysts.
 
Biog­ra­phy — Robert (Rob) M Rioux is the Friedrich G. Helf­ferich Asso­ciate Pro­fes­sor of Chem­i­cal Engi­neer­ing at the Penn­syl­va­nia State Uni­ver­si­ty. Pri­or to join­ing the Penn­syl­va­nia State Uni­ver­si­ty in 2008, he was a Nation­al Insti­tutes of Health Post­doc­tor­al Fel­low at Har­vard Uni­ver­si­ty in the Depart­ment of Chem­istry and Chem­i­cal Biol­o­gy work­ing with Pro­fes­sor George White­sides. He received his Ph.D. in phys­i­cal chem­istry from the Uni­ver­si­ty of Cal­i­for­nia, Berke­ley in 2006 work­ing for Pro­fes­sor Gabor Somor­jai. He holds a B.S. and M.S. degree in chem­i­cal engi­neer­ing from Worces­ter Poly­tech­nic Insti­tute and the Penn­syl­va­nia State Uni­ver­si­ty, respec­tive­ly. Since join­ing the Penn. State fac­ul­ty, he has received a num­ber of awards, includ­ing a DARPA Young Fac­ul­ty Award, an Air Force Office of Sci­en­tif­ic Research Young Inves­ti­ga­tor Pro­gram Award, a NSF CAREER Award and a 3M Non-Tenured Fac­ul­ty Award. Research in his lab­o­ra­to­ry is cur­rent­ly spon­sored by NSF, DOE-BES, DARPA, AFOSR, AFRL, ACS-PRF and indus­try. His group’s cur­rent research focus is on the devel­op­ment of spa­tial­ly- and tem­po­ral­ly-resolved spec­tro­scop­ic tech­niques for imag­ing cat­alyt­ic chem­istry, sin­gle mol­e­cule meth­ods to under­stand sin­gle molecule/particle cat­alyt­ic kinet­ics and dynam­ics, elu­ci­dat­ing reac­tion mech­a­nisms in nanoscale sys­tems, includ­ing cat­a­lyst syn­the­sis, devel­op­ment of solu­tion calori­met­ric tech­niques to under­stand cat­alyt­ic process­es at the sol­id-liq­uid inter­face and the devel­op­ment of base-met­al cat­a­lysts for chemos­e­lec­tive chem­i­cal trans­for­ma­tions, includ­ing bio­mass to chem­i­cals con­ver­sion.