Carbon Reactions

 

FSC 506

Spring 2012

TR 8:00-9:15 A.M.

025 Deike Building

 

 

Instructor:      L. R. Radovic,  Professor of Energy and Mineral Engineering

                        205 Hosler Building (phone: 863-0594; e-mail: LRR3@psu.edu)

 

Contents:       The basic tools of physical chemistry, chemical thermodynamics, kinetics, transport phenomena and materials science are used to discuss the formation, properties and reactivity of the ever important and increasingly diverse group of carbon materials, which range all the way from coals to the undesirable soot, from carbon blacks and activated carbons to graphite (or graphene!), as well as the highly coveted diamonds and the recently discovered fullerenes, nanotubes. Is there another material (or even subject matter) in this world that has been awarded two Nobel prizes, over a span of less than two decades?!

 

Approach:      In addition to providing a brief overview of the topics summarized below, this course is PRIMARILY meant to be an exercise in the methodology of reading and writing scientific publications.  Each topic will be covered by analyzing a specific paper (recent or classic).  The background for each paper will be provided in class and it will be reinforced by reading selected cited references.  The impact of each paper will be assessed by analyzing selected citing references. (Note: When the class enrollment allows it, the selection of topics to be discussed is adjusted to accommodate the specific interests of the students.)  

 

Homage:         This course is a direct ‘descendant’ of the legendary lectures (with the same title and same number) by Prof. Philip L. Walker, who died on March 22, 2009. It is offered in fond memory of the priceless lessons that Prof. Walker instilled in this instructor and in many other ‘disciples’ worldwide: the passion and the joy of learning and intellectual honesty in the pursuit of excellence. Prof. Walker’s entire research opus is available here. A Festschrift issue of the Carbon journal honoring Prof. Walker was published in 1991 (Vol. 29, No. 6, www.elsevier.com/locate/carbon).

 

 

A.    Fundamentals

 

1.    Formation of Carbons

       (a) Gas-phase reactions (pyrolysis, CVD)

       (b) Liquid-phase reactions (carbonization)

       (c) Solid-phase reactions (thermal decomposition)

 

2.    Structure and Characterization of Carbons

       (a) Bulk properties (chemical bonding, crystallinity, morphology)

       (b) Surface properties

            -physics

            -chemistry

 

3.    Reactions of Carbons

       (a) Solid/gas reactions

       (b) Solid/liquid reactions

 

 

B.    Applications

 

       1. Gas-phase carbon products: carbon black (soot), pyrolytic carbon, diamond, fullerenes, nanotubes

       2. Liquid-phase carbon products: coke, graphite, carbon fibers and composites

       3. Solid-phase carbon products: molecular sieves, activated carbons, catalyst supports

       4. Miscellaneous: carbon electrodes, regeneration of coked catalysts, catalysts.

 

Introduction to the literature: Chemistry and Physics of Carbon series of monographs (vols. 1-31), Marcel Dekker, 1965-2012.

 

Template for Semester Paper

            -Proposed TITLE due as early as possible (in Angel dropbox), final version by February 29.

            -Proposed OUTLINE (Table of Contents) – preferably including the preliminary List of References as well as the selected paper for detailed analysis -- due before March 15.

                        -Discussion of general issues:

                                    -by subtopic (=> judicious selection of subsections...)

                                    -sequencing of papers to be discussed

                                                -by concept (preferable!?)

                                                -in chronological order (smooth transitions?!)

            -Complete draft of PAPER due as early as possible, no later than April 15.

            -Individual discussions (15 min-1 h) of the current draft during the week of 4/16.

            -Final version of PAPER due by May 4.

 

 

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Here is an example of previous class discussions of papers:

 

A study of citing papers, both formal and substantive, is a very important (and too often neglected) exercise. Let’s update this graph for the classical paper by Rosalind Franklin (Proc Roy Soc A209, 1951, 196-218). Comments?

 

It’s good practice to redraw important graphs from papers that are important for one’s own research. Here’s one from Franklin’s paper. Do ALL the data points correspond to the numbers shown in the relevant table? (Are both the table and the figure necessary?)


Title: THE SURFACE STRUCTURE AND REACTIVITY OF BLACK CARBON
Author(s): SMITH DM, CHUGHTAI AR
Source: COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS 105 (1): 47-77 DEC 1 1995

Here is one version of the annotated MS… for Thursday discussion.

Some specific discussion issues:

-Did Smith and Chughtai really perform “BET adsorption measurements”, as claimed by Smekens et al. (2005)?

-Müller et al. (2005) say that “oxygen containing [sic] functional groups attached to non-six-membered rings may occur as very reactive sites [17]”, where Ref. 17 is the Smith and Chughtai paper. Comments about this citation?

-Zawadzki et al. (2003) also studied the carbon-NO2 reaction using IR spectroscopy. Did they make, and should they have made, any SUBSTANTIVE comments about the results or findings of Smith and Chughtai?
-Chughtai et al. (2002) say the following: “The band at 1725 cm-1 … is due to carboxylic species whose absorbance reflects the state of oxidation (Smith and Chughtai, 1995).” Based on this statement, what exactly should we expect to find in Smith and Chughtai (1995)? (In which figure/table is the relevant evidence provided?)

-Mawhinney and Yates (2001) say that the “O3-induced formation of [carboxyl] groups has been discussed in [the] literature where the creation of anhydride groups is followed by reaction with water to form two COOH groups.” One of the cited references is Smith and Chughtai (1995). How are the two proposed mechanisms related, if at all? (So, in what context, and for what purpose, is the ‘mechanism’ proposed by Smith and Chughtai (1995) cited here?)

-Kirchner et al. (2000) also studied the kinetics of the soot-NO2 reaction using FTIR. Did they compare their findings with those of Smith and Chughtai (1995)? If yes, was the comparison ‘favorable’? If not, why not?

-Since very little (if any) direct or even circumstantial evidence is presented in this paper (do you agree?), please check at least one or two of the cited reference and see whether you can find there such evidence for some of the more important arguments? For example, what is the message of Figure 5 (which occupies almost an entire page)? How much text do the authors devote to its discussion? Does this figure really show what the authors say it (presumably) shows? Hopefully the original reference says something more profound…

 

One “bottom line” conclusion from our analysis of the Smith and Chughtai (1995) paper is that their ‘cartoons’ (Figs. 10 and 11) are intuitive (as most ‘cartoons’ indeed are). How insightful are they? The jury is still out, and only time will tell (partly based on the authority and ‘credibility’ of the authors)… For VERY insightful cartoons that have withstood the test of time admirably, see R E Franklin, Proc Roy Soc London 1951, A209 (1097), 196-218 (available online through JSTOR). 

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Spring 2012 Schedule:

 

-Weeks of 01/09, 01/16 and 01/23: ‘Classic’ paper(s) and paper selection process.

            “Use of N2 vs. CO2 in the Characterization of Activated Carbons”, Langmuir 3, 1987, 76-81.

            “Shock-Tube Measurements of Soot Oxidation Rates”, Combustion & Flame 20, 1973, 369-379.

 

-Week of 01/30. Paper 1: “Surface chemistry, pore sizes and adsorption properties of activated carbon fibers and precursors treated with ammonia”, Carbon 39, 2001, 1809-1820.

            -Here are some discussion topics:

                        (1) Do the numbers in the last column of Tables 3 and 5 agree with the information provided elsewhere in these tables (and in this paper)?
                        (2) Is there a correlation between average pore size and specific surface area (e.g., in Tables 2 and 4)? Should such a correlation exist? What do the authors say about this issue?

                        (3) Do the results shown in Figures 1 and 2 agree with the results shown elsewhere in the paper?

                        (4) Do XPS results (Table 6) for N agree with the elemental analysis (Tables 3 and 5)? Should they? Do the authors discuss this issue?

                        (5) Do the results in the last column of Table 6 make sense? Do the authors discuss them?
                        (6) Contrary to what I said on Tuesday, there IS a clear rationale for the selection of samples in Figures 8-11! But does the uptake of HCl really correlate with some parameter that is affected, or that can be controlled, by ammonia treatment? (Can we construct such a graph, which would be analogous to Figure 13?) And do any of the citing papers discuss this key issue (effects of porosity vs. surface chemistry on the AMOUNT of pollutant adsorbed AND on the AFFINITY of the surface for the pollutant)? What is the (subtle?) difference between AMOUNT and AFFINITY? (Does the latter automatically affect the former? In what way? Physical chemistry 101?) 

                        (7) The maximum measured uptake of HCl is 14 wt% (at ca. 5000 ppmv). Is this more or less than a ‘monolayer’, and what are the implications of this fact for the discussion regarding reversibility or controlling mechanism of HCl adsorption? Do the authors discuss this?

                        (8) Do the authors explain how they obtained the last two columns in Table 8? Are ALL the numbers from Table 8 shown in Figure 13? And does that matter?

                        (9) If the “adsorption is completely reversible and must therefore involve enhanced physical adsorption instead of chemisorption” (p1809), should there exist a correlation between N content and HCl uptake that would justify the conclusion that the “adsorption of an acidic contaminant (HCl) was shown to be greatly enhanced by treating the fibers with ammonia to create a basic surface” (p1819)? (See also #6 above.)

 

-Week of 02/06: “Acidic and basic sites on the surface of porous carbons”, Carbon 35, 1997, 1361-1366.

            -see Angel dropbox for one version of annotated paper.

            -here is the SCI summary of citing papers.

 

-Week of 02/13: Individual discussions of the title of semester paper.

 

-Week of 02/20: “Synthesis and systematic characterization of functionalized graphene sheets generated by thermal exfoliation at low temperature”, J Phys D 43, 2010, 275402.

            -here is an example of the initial annotation.

            -and here is the SCI summary of papers with “graphite oxide” in the title.

           

Whether a study, and a paper that describes it, can withstand close(r) scrutiny is a VERY important part of the (hopefully scientific) research enterprise. The more ambitious (and/or interesting) the claims of the authors, the more likely it is that their study will undergo such scrutiny. (Familiar with the “cold fusion” fiasco? And in the carbon field, the bold soccer-ball proposal for the structure of C60 was viewed with initial skepticism by some scientists, but in the end it was awarded the Nobel Prize in Chemistry…) An example of such scrutiny is provided below for the Jin et al. paper (see above).

            -To support their (outrageous?) statement that the characteristic DTG peak observed near 292 oC corresponds to “the burning temperatures of functional groups such as hydroxyl, carboxyl and epoxide groups”, the authors direct the reader to their own 2009 J Phys D paper entitled “Tailoring the characteristics of graphite oxides by different oxidation times”. (Note that the title of this paper suggests that J Phys D is NOT the appropriate forum for a meaningful discussion of such “chemistry-oriented” issues, and its analysis – see below – confirms such assessment.)

            -The (most?) relevant (and presumably supporting) statements in this cited paper is the following: “The first two dominant peaks (2 and 3) near 200 and 230 oC are ascribed to the burning of functional groups… Peak 2 has a burning temperature near 200 oC, which can be assigned to hydroxyl groups.” This last statement refers the reader (unbelievably!!!) to a paper whose title is “Thermal desorption of n-alcohols intercalated in vanadium pentoxide-hydrate”!? The subsequent statement is even more outrageous -- unless substantiated VERY carefully (see below) -- because it goes against physical/organic chemistry 101 and ignores everything we know about carbon surfaces: “Peak 3 has a higher burning temperature than peak 2, and therefore could have a strong bond that can be attributed to carboxyl groups [Boehm, Carbon 40, 145, 2002], since the double bond between carbon and oxygen of the carboxyl group should be stronger than the single bond between carbon and oxygen of the hydroxyl group.” Wow!!!!!!!!!!!!!! If the authors really read Boehm’s papers – and citing Boehm’s 2002 paper in this context borders on deception (and not just unacceptable lack of knowledge) – they would know what every carbon researcher knows: (1) hydroxyl surface functional groups are much more stable than carboxyl groups; (2) the latter decompose to form CO2 and therefore the relevant bond strength comparison is between the C-C bond in Ar-COOH and the C-O bond in Ar-OH. (The only way that the argument advanced by the authors could make sense is if, somehow, the fate of surface functionalities in the presence of O2 were drastically different from what is known to occur upon exposure to elevated temperature during their desorption; thus, O2 would have to ‘attack’ the C=O bond in the carboxyl group, as well as the C-O  bond in the hydroxyl group, before this group decomposes/desorbs. A well designed “blank experiment”, using, say, TGA/MS, could resolve that, especially because the proposed low-temperature exfoliation process is carried out “under ambient Ar” (that is, in inert atmosphere, and NOT in air.)

            -When such flaws (or such omissions) are detected in the arguments of the authors, it is doubtful how much useful information can be rescued from the rest of their study, at least when it comes to the interpretation of the results, but also perhaps when it comes to the reliability of the results.

 

-Week of 02/27: “‘Molecular Basket’ Sorbents for Separation of CO2 and H2S from Various Gas Streams”, JACS 131, 2009, 5777-5783.

 

-Week of 03/12: Individual discussions of the outline of semester paper.

            -Rescheduled for week of 03/26 (see below).

 

-Thursday, 03/22: “Ultra-deep desulfurization and denitrogenation of diesel fuel by selective adsorption over different adsorbents: A study on adsorptive selectivity and mechanism”, Catalysis Today, 111 (2006), 74-83.

            -Here are some annotations to spark our in-class discussion!

 

-Week of 03/26: Individual discussions of the (revised?) outline of semester paper, with special emphasis on your List of References.

 

-Weeks of 04/02, 04/09 and 04/16: Individual discussions of the draft of semester paper.

 

 

LRR3@psu.edu (updated 03/26/2012, 21:15)