How can the modern scanning transmission electron microscope aid catalysis science?

Novem­ber 2018
Prof. Eric A. Stach
Uni­ver­si­ty of Penn­syl­va­nia
E-mail: stach@​seas.​upenn.​edu, Web:https://stachgroup.seas.upenn.edu/
Abstract: The past decade or so have seen a num­ber of tech­no­log­i­cal advances in the field of trans­mis­sion elec­tron microscopy that have dra­mat­i­cal­ly enhanced both the util­i­ty and uti­liza­tion of the instru­ment in the field of het­ero­ge­neous catal­y­sis. These include aber­ra­tion cor­rec­tion, enhanced detec­tors and improve­ments in sim­u­la­tion and analy­sis soft­ware. In this pre­sen­ta­tion, I will present sev­er­al spe­cif­ic exam­ples from both my own research and from oth­ers in the field to pro­vide a gen­er­al overview of the state of the art. In spe­cif­ic, I will describe the lim­its of spa­tial, spec­tro­scop­ic and tem­po­ral ener­gy res­o­lu­tion, and demon­strate how one can per­form both real time and operan­do mea­sure­ments do char­ac­ter­ize the inter­re­la­tion­ships between cat­a­lyst struc­ture and cat­a­lyst func­tion. Through the pre­sen­ta­tion, I will empha­size how these tech­niques are being imple­ment­ed at the Singh Cen­ter for Nan­otech­nol­o­gy at the Uni­ver­si­ty of Penn­syl­va­nia and how they are thus acces­si­ble to mem­bers of the Cat­a­lyst Club of Philadel­phia.

Ultra-Deep Diesel Hydrodesulfurization Catalysis and Process: A Tale of Two Sites

Octo­ber 2018 — F.G. Cia­pet­ta Award Lec­ture

Dr. Teh C. Ho
Hydro­car­bon Con­ver­sion Tech­nolo­gies
E-mail: , Web:
Abstract: Hydrodesul­fu­r­iza­tion cat­a­lysts have two types of active sites for hydro­gena­tion and hydrogenol­y­sis reac­tions. While hydro­gena­tion sites are more active for desul­fu­r­iz­ing refrac­to­ry sul­fur species, they are more vul­ner­a­ble to organon­i­tro­gen inhi­bi­tion than hydrogenol­y­sis sites. In con­trast, hydrogenol­y­sis sites are less active for desul­fu­r­iz­ing refrac­to­ry sul­fur species but are more resis­tant to organon­i­tro­gen inhi­bi­tion. This dichoto­my is exploit­ed to devel­op an ultra-deep hydrodesul­fu­r­iza­tion stacked-bed reac­tor com­pris­ing two cat­a­lysts of dif­fer­ent char­ac­ter­is­tics. The per­for­mance of this cat­a­lyst sys­tem can be supe­ri­or or infe­ri­or to that of either cat­a­lyst alone. A the­o­ry is devel­oped to pre­dict the opti­mum stack­ing con­fig­u­ra­tion for max­i­mum syn­er­gies between the two cat­a­lysts. The best con­fig­u­ra­tion pro­vides the pre­cise envi­ron­ment for the cat­a­lysts to reach their full poten­tials, result­ing in the small­est reac­tor vol­ume and max­i­mum ener­gy sav­ing. Mod­el pre­dic­tions are con­sis­tent with exper­i­men­tal results. A selec­tiv­i­ty-activ­i­ty dia­gram is devel­oped for guid­ing the devel­op­ment of stacked-bed cat­a­lyst sys­tems.

Catalysis by Pincer-Iridium Complexes. Breaking C-H Bonds, Making C-C Bonds, and Various Combinations Thereof

Sep­tem­ber 2018

Pro­fes­sor Alan S. Gold­man
Depart­ment of Chem­istry and Chem­i­cal Biol­o­gy, Rut­gers — The State Uni­ver­si­ty of New Jer­sey
E-mail: alan.​goldman@​rutgers.​edu, Web: http://​ccb​.rut​gers​.edu/​g​o​l​d​m​a​n​-​a​lan
Abstract: Irid­i­um com­plex­es have played a lead­ing role in the organometal­lic chem­istry of
alka­nes and unre­ac­tive C-H bonds since the incep­tion of the field 30 years ago. We have found
that “PCP”-pincer-ligated irid­i­um com­plex­es are par­tic­u­lar­ly effec­tive for the dehy­dro­gena­tion of
alka­nes and have incor­po­rat­ed this reac­tion into tan­dem sys­tems for sev­er­al cat­alyt­ic
trans­for­ma­tions based on dehy­dro­gena­tion. A close­ly relat­ed class of reac­tions that we are
explor­ing is dehy­dro­gena­tive cou­pling. More recent­ly we have turned atten­tion to irid­i­um
Phe­box com­plex­es. Although the (PCP)Ir and (Phebox)Ir units are for­mal­ly iso­elec­tron­ic, the
for­mer oper­ates via C-H acti­va­tion by Ir(I) while the lat­ter effects dehy­dro­gena­tion via Ir(III) (as
an acetate com­plex) and pos­si­bly Ir(V) inter­me­di­ates. Such a high-oxi­da­tion-state cat­alyt­ic cycle
offers advan­tages for many poten­tial appli­ca­tions of dehy­dro­gena­tion. In par­al­lel, how­ev­er, we
find that the low-oxi­da­tion-state (+I) chem­istry of (Phebox)Ir offers its own nov­el hydro­car­bon
chem­istry.
1. Gao, Y.; Guan, C.; Zhou, M.; Kumar, A.; Emge, T. J.; Wright, A. M.; Gold­berg, K. I.; Krogh-Jes­persen, K.; Gold­man, A. S. J. Am. Chem. Soc. 2017,
139, 6338–6350.
2. Wilk­low-Mar­nell, M.; Li, B.; Zhou, T.; Krogh-Jes­persen, K.; Bren­nes­sel, W. W.; Emge, T. J.; Gold­man, A. S.; Jones, W. D. J. Am. Chem. Soc. 2017,
139, 8977–8989.
3. Gold­berg, K. I.; Gold­man, A. S. Acc. Chem. Res. 2017, 50, 620–626.
4. Kumar, A.; Bhat­ti, T. M.; Gold­man, A. S. Chem. Rev. 2017, 117, 12357–12384.
5. Gao, Y.; Emge, T. J.; Krogh-Jes­persen, K.; Gold­man, A. S. J. Am. Chem. Soc. 2018, 140, 2260–2264.

Renewable Isoprene By Sequential Hydrogenation of Itaconic Acid and Dehydra-Decyclization of 3-Methyl-Tetrahydrofuran

2018 Spring Symposium

Omar Abdel­rah­man, Post-Doc, Paul Dauen­hauer Group, Depart­ment of Chem­i­cal Engi­neer­ing & Mate­r­i­al Sci­ence, Uni­ver­si­ty of Min­neso­ta, 421 Wash­ing­ton Ave. SE, Min­neapo­lis, MN 55455

Abstract — The cat­alyt­ic con­ver­sion of bio­mass-derived feed­stocks to val­ue added chem­i­cals is an impor­tant chal­lenge to alle­vi­ate the depen­dence on petro­le­um-based resources. To accom­plish this, the inher­ent­ly high oxy­gen con­tent of bio­mass com­pounds, such as that of lig­no­cel­lu­losic bio­mass, requires sig­nif­i­cant reduc­tion via hydrodeoxy­gena­tion strate­gies. The unsat­u­rat­ed car­boxylic acid ita­con­ic acid (IA) can be pro­duced from bio­mass via fer­men­ta­tion path­ways, for exam­ple. A path­way of inter­est is the con­ver­sion of IA to iso­prene, facil­i­tat­ing the renew­able pro­duc­tion of an indus­tri­al­ly rel­e­vant diolefin. IA can be suc­ces­sive­ly hydro­genat­ed to yield 3-methyl tetrahy­dro­fu­ran (3-MTHF), in a one-pot cas­cade reac­tion, where a Pd-Re bimetal­lic cat­a­lyst results in an 80% yield to 3-MTHF. The 3-MTHF can then be con­vert­ed to iso­prene, and oth­er pen­ta­di­enes, through an acid cat­alyzed vapor-phase dehy­dra-decy­cliza­tion. Mul­ti­ple sol­id acid cat­a­lysts, includ­ing alu­mi­nosil­i­cates, met­al oxides and phos­pho­rous mod­i­fied zeo­lites, were screened for the dehy­dra-decy­cliza­tion step. A new class of cat­alyt­ic mate­ri­als, all sil­i­con
phos­pho­rous con­tain­ing zeo­lites, were found to be the most selec­tive (70% iso­prene and 20% pen­ta­di­enes), where the major side reac­tion involved is a retro-prins con­den­sa­tion of 3-MTHF to butane and formalde­hyde. Through kinet­ic stud­ies, an inves­ti­ga­tion into the effect of Brøn­st­ed acid strength, pore size and oper­at­ing con­di­tions on the selec­tiv­i­ty to iso­prene are dis­cussed. The prospect of apply­ing this dehy­dra-decy­cliza­tion strat­e­gy to oth­er sat­u­rat­ed cyclic ethers will also be dis­cussed, which enables the pro­duc­tion of oth­er diolefin mol­e­cules of inter­est such as buta­di­ene and lin­ear pen­ta­di­enes.

Ref­er­ences:
[1] Abdel­rah­man, O. A.; Park, D. S.; Vin­ter, K. P.; Span­jers, C. S.; Ren, L.; Cho, H. J.; Zhang, K.; Fan, W.; Tsap­at­sis, M.; Dauen­hauer, P. J. ACS Catal. 2017, 7, 1428–1431.

Using Water as a Co-catalyst in Heterogeneous Catalysis to Improve Activity and Selectivity

2018 Spring Symposium

Lars C. Grabow, Depart­ment of Chem­i­cal and Bio­mol­e­c­u­lar Engi­neer­ing, Uni­ver­si­ty of Hous­ton, Hous­ton, TX 77204–4004, USA

Abstract — “What hap­pens when you add water?” is pos­si­bly the most fre­quent­ly asked ques­tion after pre­sen­ta­tions in het­ero­ge­neous catal­y­sis. In this talk, I will demon­strate that this ques­tion is indeed para­mount and that the pres­ence of even minute amounts of water can dras­ti­cal­ly change reac­tion rates and prod­uct selec­tiv­i­ties. Exam­ples include water-medi­at­ed pro­ton hop­ping across a met­al-oxide sur­face, oxi­da­tion of car­bon monox­ide at the gold/titania inter­face, and hydrodeoxy­gena­tion of phe­no­lic com­pounds over tita­nia sup­port­ed ruthe­ni­um cat­a­lysts. Togeth­er, these exam­ples demon­strate that water can act as co-cat­a­lyst in a vari­ety of cat­alyt­ic reac­tions and by vary­ing the amount of water it may be pos­si­ble to tune reac­tion rates and prod­uct selec­tiv­i­ty.

Selective Catalytic Oxidation of Alcohols over Supported Metal Nanoparticles and Atomically-Dispersed Metal Cations

2018 Spring Symposium

Robert J. Davis, Depart­ment of Chem­i­cal Engi­neer­ing, Uni­ver­si­ty of Vir­ginia, Char­lottesville, VA, USA

Abstract — Selec­tive oxi­da­tion of alco­hols to car­bonyl com­pounds is an impor­tant reac­tion in organ­ic syn­the­sis and will like­ly play a sig­nif­i­cant role in the devel­op­ment of val­ue-added chem­i­cals from bio­mass. The indus­tri­al appli­ca­tion of a pre­cious met­al cat­a­lyst such as Pt, how­ev­er, can be hin­dered by deac­ti­va­tion and high price. We have there­fore explored the mode of deac­ti­va­tion dur­ing alco­hol oxi­da­tion on Pt by in-situ spec­troscopy and stud­ied the role of var­i­ous pro­mot­ers on cat­a­lyst per­for­mance. Results con­firm that slow decar­bony­la­tion of prod­uct alde­hyde deposit­ed unsat­u­rat­ed hydro­car­bon on the sur­face that blocked access to the active sites. Addi­tion of Bi as a pro­mot­er did not pre­vent the decar­bony­la­tion side reac­tion, but instead enhanced the acti­va­tion of dioxy­gen dur­ing the cat­alyt­ic cycle. In an effort to avoid the use of pre­cious met­als alto­geth­er, the oxi­da­tion of alco­hols over atom­i­cal­ly-dis­persed, non-pre­cious met­al cations (Fe, Cu, and Co) locat­ed in a nitro­gen-doped car­bon matrix was demon­strat­ed. Exten­sive char­ac­ter­i­za­tion of these non-pre­cious met­al cat­a­lysts revealed impor­tant insights into the oxi­da­tion mech­a­nism and sta­bil­i­ty of this new class of atom­i­cal­ly-dis­persed met­al cat­a­lyst.

Tuning the Electrocatalytic Oxygen Reduction Reaction Activity of PtCo Nanocrystals by Cobalt Concentration and Phase Transformation Methods

2018 Spring Symposium

Jen­nifer D. Lee, Ph.D. Can­di­date, Christo­pher B. Mur­ray Group, Depart­ment of Chem­istry, Uni­ver­si­ty of Penn­syl­va­nia

Abstract — The pro­ton exchange mem­brane fuel cell (PEMFC) is a crit­i­cal tech­nol­o­gy to enhance the clean, sus­tain­able pro­duc­tion and usage of ener­gy, but prac­ti­cal appli­ca­tion remains chal­leng­ing because of the high cost and low dura­bil­i­ty of the cath­ode cat­a­lysts that per­form oxy­gen reduc­tion reac­tion (ORR). Efforts have been placed on the study of intro­duc­ing first-row tran­si­tion met­als in Pt-M alloys to reduce the Pt load­ing and mod­u­late geo­met­ric, struc­tur­al and elec­tron­ic effects. To fur­ther improve the ORR reac­tion rate and cat­a­lysts sta­bil­i­ty, alloys that adopt an inter­metal­lic struc­ture, espe­cial­ly the tetrag­o­nal L10-PtM phase, has been one of the most promis­ing mate­ri­als. In this con­tri­bu­tion, monodis­perse PtCo nanocrys­tals (NCs) with well-defined size and Co com­po­si­tion are syn­the­sized via solvother­mal meth­ods. The trans­for­ma­tion from face-cen­tered cubic (fcc) to ordered face-cen­tered tetrag­o­nal (fct) struc­ture was achieved via ther­mal anneal­ing. Depend­ing on the selec­tion of trans­for­ma­tion meth­ods, dif­fer­ent degrees of order­ing were intro­duced and fur­ther cor­re­lat­ed with their ORR per­for­mance. A detailed study of the anneal­ing tem­per­a­ture and com­po­si­tion depen­dent degree of order­ing is also high­light­ed. This work pro­vides the insight of dis­cov­er­ing the opti­mal spa­tial dis­tri­b­u­tions of the ele­ments at the atom­ic lev­el to achieve enhanced ORR activ­i­ty and sta­bil­i­ty.