2009 Spring Symposium

 
Jochen Lauter­bach
Depart­ment of Chem­i­cal Engi­neer­ing
Uni­ver­si­ty of Delaware
Newark, DE

Abstract — We have been using high-through­put (HT) approach­es based on rapid-scan FTIR hyper­spec­tral imag­ing in the mid-infrared to screen cat­a­lyst for­mu­la­tions for the dis­cov­ery and opti­miza­tion of new and improved mate­ri­als. In com­bi­na­tion with HT meth­ods, we also employ a vari­ety of more tra­di­tion­al spec­tro­scop­ic meth­ods to under­stand the under­ly­ing fun­da­men­tal sci­ence.

Two exam­ples will be used to illus­trate this research approach: de-NOx for auto­mo­tive exhaust after-treat­ment and ammo­nia decom­po­si­tion cat­a­lysts for CO free hydro­gen generation.While HT screen­ing is a macro­scop­ic analy­sis tech­nique, we are also inter­est­ed in observ­ing non-lin­ear phe­nom­e­na on work­ing cat­a­lysts in situ on the microscale using spec­tro­scop­ic imag­ing based on ellip­som­e­try. The col­lec­tive, glob­al behav­iour of a cat­alyt­ic sys­tem depends on the effec­tive com­mu­ni­ca­tion of local reac­tiv­i­ty vari­a­tions to dis­tant points in the sys­tem. One mode of com­mu­ni­ca­tion occurs via par­tial pres­sure fluc­tu­a­tions in the gas-phase above the cat­alyt­i­cal­ly active sur­face. This gas-phase cou­pling mode is con­sid­ered to be most effec­tive under vac­u­um con­di­tions, where the mean free path between mol­e­c­u­lar col­li­sions is large. We take advan­tage of a spa­tial­ly dis­trib­uted sys­tem of iso­lat­ed chem­i­cal oscil­la­tors to inves­ti­gate the details of gas-phase com­mu­ni­ca­tion in the 10–3 Torr range. Char­ac­ter­i­za­tion of local gas-phase vari­a­tions, in con­junc­tion with local kinet­ic activ­i­ty on the sur­face, shows that sur­face/­gas-phase inter­ac­tion might dif­fer from the con­ven­tion­al assump­tion of a gra­di­ent free, mol­e­c­u­lar flow envi­ron­ment near the sur­face. This analy­sis pro­vides a quan­ti­ta­tive esti­mate of the effec­tive gas-phase cou­pling length in a het­ero­ge­neous sys­tem. This cou­pling length was found to be in agree­ment with sur­face imag­ing results which qual­i­ta­tive­ly showed cou­pling between oscil­la­tors.

Speaker’s Biog­ra­phy — Jochen Lauter­bach received his Diplo­ma in Physics at the Uni­ver­si­ty of Bayreuth, Ger­many under Prof. J. Küp­pers and his Doc­tor­ate in Phys­i­cal Chem­istry at the Fritz-Haber Insti­tute of the Max-Planck-Soci­ety, Berlin, Ger­many under Pro­fes­sor G. Ertl. He came to the US in 1994 with a Feodor-Lynen-Fel­low­ship of the Alexan­der von Hum­boldt-Foun­da­tion and per­formed his post-doc­tor­al work at the Uni­ver­si­ty of Cal­i­for­nia at San­ta Bar­bara under Prof. W.H. Wein­berg. He joined the fac­ul­ty at Pur­due in 1996 and, in 2002, moved to the Uni­ver­si­ty of Delaware, where he cur­rent­ly is a Pro­fes­sor in the Chem­i­cal Engi­neer­ing Depart­ment. His research inter­ests include the design of cat­alyt­ic mate­ri­als using high-through­put screen­ing method­olo­gies and in situ spec­tro­scop­ic tech­niques, devel­op­ment of cat­a­lyst syn­the­sis method­olo­gies based on microemul­sions, nano-engi­neered poly­mer films from renew­able feed­stock, and non-lin­ear dynam­ics of chem­i­cal reac­tions, in par­tic­u­lar exter­nal spa­tiotem­po­ral forc­ing. Pro­fes­sor Lauter­bach has pub­lished close to 100 papers/book chap­ters and has giv­en over 150 invit­ed pre­sen­ta­tions.

2009 Spring Symposium

 
Gary Haller
Depart­ment of Chem­istry
Yale Uni­ver­si­ty
New Haven, CT

Abstract — Mobil com­po­si­tion of mate­r­i­al No. 41 (MCM-41) was dis­closed in 1992 and short­ly after a research project was ini­ti­at­ed at Yale to use these mate­ri­als to demon­strate a radius of cur­va­ture effect on cat­alyt­ic activ­i­ty. The “radius of cur­va­ture” effect implies a change in the sol­id sur­face ten­sion of the pore wall as the pore diam­e­ter (cur­va­ture) is changed that is expect­ed to change the activity/selectivity of an iso­lat­ed cat­alyt­ic site on the pore wall of the sup­port. An iso­lat­ed site can be formed by iso­mor­phous sub­sti­tu­tion (dur­ing syn­the­sis) of some Si cations by V cations in the MCM-41 sil­i­ca matrix. Sev­er­al labs have report­ed that iso­lat­ed V sites on a sil­i­ca sup­port are prefer­able to dimers, oligomers or poly­mers of van­dia on a sil­i­ca sup­port for the oxi­da­tion of methanol to formalde­hyde. MCM-41 might have an advan­tage rel­a­tive to oth­er sil­i­cas because of its very high sur­face area, >1000 m²/g. Both the air oxi­da­tion of methanol and methane to formalde­hyde have been used as probe reac­tions for cat­alyt­ic char­ac­ter­i­za­tion of V-MCM-41. SBA-15 has a sim­i­lar struc­ture to MCM-41, but larg­er pores and thick­er walls. Iso­mor­phous sub­sti­tu­tion of V dur­ing syn­the­sis is not prac­ti­cal, but well dis­persed V can be pre­pared post-syn­the­sis by graft­ing (reac­tion with sur­face hydrox­yls). The activ­i­ty for methanol oxi­da­tion on V-MCM-41 and V-SBA-15 will be com­pared and dis­cussed.

Speaker’s Biog­ra­phy — Gary L. Haller is the Hen­ry Pren­tiss Bec­ton Pro­fes­sor of Engi­neer­ing and Applied Sci­ence at Yale Uni­ver­si­ty with joint appoint­ments in the Depart­ments of Chem­i­cal Engi­neer­ing and Chem­istry. Pro­fes­sor Haller received a B.S. in math­e­mat­ics and chem­istry from the Uni­ver­si­ty of Nebras­ka at Kear­ney in 1962 and a Ph.D. in phys­i­cal chem­istry from North­west­ern Uni­ver­si­ty in 1966. Fol­low­ing a NATO Post-doc­tor­al Fel­low­ship at Oxford Uni­ver­si­ty, he joined the fac­ul­ty of Yale where he has held a vari­ety of admin­is­tra­tive posts that include Chair of the Depart­ment of Chem­i­cal Engi­neer­ing, Chair of the Coun­cil of Engi­neer­ing, and Deputy Provost for Phys­i­cal Sci­ences and Engi­neer­ing. He was Mas­ter of Jonathan Edwards Col­lege, one of twelve res­i­den­tial col­leges that com­prise Yale Col­lege 1997–2008.

Pro­fes­sor Haller’s research involved the mol­e­c­u­lar under­stand­ing of het­ero­ge­neous cat­a­lysts. His research com­bines the inor­gan­ic chem­istry of cat­a­lyst syn­the­sis, phys­i­cal chem­istry of spec­tro­scop­ic char­ac­ter­i­za­tion of het­ero­ge­neous cat­a­lysts, and the kinet­ics and mech­a­nism of sim­ple organ­ic reac­tions. Cur­rent research is focused on cat­a­lysts for the syn­the­sis of sin­gle walled car­bon nan­otubes and the appli­ca­tion of these car­bon nan­otubes as sup­ports for nov­el cat­alyt­ic reac­tions such as aque­ous phase reform­ing (a route to renew­able ener­gy sources).

2009 Spring Symposium

 
Danielle A. Hans­gen
Depart­ment of Chem­i­cal Engi­neer­ing
Uni­ver­si­ty of Delaware
Newark, DE

Abstract — The ammo­nia decom­po­si­tion reac­tion has recent­ly received increased atten­tion due to the pos­si­bil­i­ty of ammo­nia being used as a hydro­gen stor­age medi­um in a pos­si­ble hydro­gen econ­o­my. We have explored this decom­po­si­tion reac­tion through mul­ti­scale micro­ki­net­ic mod­el­ing for a num­ber of tran­si­tion met­al cat­a­lysts, includ­ing Cu, Pt, Ir, Ru, Pd, Rh, Co, Ni, Fe, W, and Mo, to bet­ter under­stand the reac­tion mech­a­nism. An under­stand­ing of the reac­tion mech­a­nism and elec­tron­ic prop­er­ties of these met­als has giv­en insight into how to tai­lor cat­a­lysts to improve cat­alyt­ic activ­i­ty for this reac­tion.

The mech­a­nism con­sists of 12 ele­men­tary reac­tion steps and 5 sur­face species, name­ly N, H, NH, NH₂, and NH₃. For many of the met­als, a large por­tion of the sur­face is cov­ered by adsor­bates. For these met­als, repul­sive adsor­bate-adsor­bate inter­ac­tions were expect­ed to change the bind­ing ener­gies of the sur­face species, there­by chang­ing the ele­men­tary reac­tion acti­va­tion bar­ri­ers and mod­i­fy­ing the cat­alyt­ic activ­i­ty [1]. Cov­er­age depen­dant atom­ic heats of chemisorp­tion were cal­cu­lat­ed through DFT using the Vien­na Ab-ini­tio Sim­u­la­tion Pack­age (VASP) for the var­i­ous tran­si­tion met­al cat­a­lysts. Cov­er­age depen­dant mol­e­c­u­lar bind­ing ener­gies were cal­cu­lat­ed using a method based on scal­ing rela­tion­ships pub­lished by Abild-Ped­er­son et al. [2] and acti­va­tion bar­ri­ers were cal­cu­lat­ed through the bond-order con­ser­va­tion (BOC) method [3].

Inclu­sion of the inter­ac­tion para­me­ters to the mod­els result­ed in reduced nitro­gen cov­er­ages and a peak shift in the vol­cano curve. The con­ver­sions were plot­ted against the char­ac­ter­is­tic nitro­gen heat of chemisorp­tion for each met­al, which was found to be an ade­quate descrip­tor for this reac­tion. The vol­cano curve of the con­ver­sions cal­cu­lat­ed through the micro­ki­net­ic mod­els are in good agree­ment with exper­i­men­tal data of sin­gle met­al cat­a­lysts by Gan­ley and cowork­ers [4]. The max­i­mum activ­i­ty was found at a nitro­gen heat of chemisorp­tion of approx­i­mate­ly 130 kcal/mol.

A DFT study of nitro­gen bind­ing ener­gies on Pt-3d bimetal­lic sur­faces showed a bind­ing ener­gy of 131 kcal/mol on the Ni-Pt-Pt sur­face, indi­cat­ing that it could be a poten­tial­ly active cat­a­lyst; there­fore sur­face sci­ence exper­i­ments were per­formed to assess the micro­ki­net­ic mod­el and DFT results. The Ni-Pt-Pt sur­face was found to be more active at decom­pos­ing ammo­nia at low tem­per­a­tures and des­orbed nitro­gen at low­er tem­per­a­tures than a Ru(0001) sur­face [5], cur­rent­ly the most active sin­gle met­al cat­a­lyst

Speaker’s Biog­ra­phy — Danielle Hans­gen received her Bachelor’s degree in chem­i­cal engi­neer­ing in 2005 from the Uni­ver­si­ty of Wash­ing­ton. She is cur­rent­ly a third year, PhD can­di­date in chem­i­cal engi­neer­ing at the Uni­ver­si­ty of Delaware. She is advised by Dr. Dion G. Vla­chos and Dr. Jing­guang G. Chen and is work­ing on the ratio­nal design of cat­a­lysts for the ammo­nia decom­po­si­tion reac­tion.