Questions tagged [catalysis]

This tag is appropriate for reactions, their mechanisms, their kinetics, when catalysts of any kind are involved.

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28
votes
1answer
616 views

How does Palladium dissociate H₂ so easily?

If I understand correctly, $\ce{H2}$ in the presence of $\ce{Pd}$ readily dissociates as it dissolves into the metal. With the dissociation energy for the $\ce{H—H}$ bond being so large, how is this ...
23
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4answers
15k views

Platinum group metals: Why are platinum and palladium great catalysts and not the others?

Platinum and palladium are great catalysts. At the same time, other metals of the so-called platinum group metals are not. What are the atomic level reasons for this?
23
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3answers
528 views

Energy-efficiency aside, what are the chemical constraints on CO₂ capture and methanation?

Synthesising $\ce {CH4}$ from air and water (in a non-biological process) has been proposed as one form of energy storage. What are the chemical constraints at play here? That is to say, what sort of ...
17
votes
1answer
660 views

What is the chemistry behind this "petrol from air" technology?

A recent news report in the UK claimed a breakthrough in making a petrol equivalent from carbon dioxide and water: A small British company has produced the first "petrol from air" using a ...
16
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4answers
29k views

Why is pyridine used when making tosyl esters from alcohols?

Tosyl chloride is used to make a hydroxyl group into a better leaving group. However, when the reaction of tosyl chloride and an alcohol occurs, a weak base such as pyridine should be used. Why?
15
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3answers
938 views

Won't the net effect of a catalyst be zero if it creates a new path with lower activation energy?

A catalyst will provide a new path with a lower activation energy (Figure 1). Won't this mean the forward and backward reactions will both speed up (as they both have a lower activation energy path to ...
15
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2answers
7k views

Difference between Lindlar and Rosenmund catalysts

Is there any difference between the Lindlar and Rosenmund catalysts? I've checked around, and it seems the same compounds are used to make both. Is there a difference in their reactivities or are they ...
14
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1answer
399 views

How does the choice of metal (oxide) catalyst affect the range of unsaturated compounds that can be hydrogenated?

In the hydrogenation of unsaturated compounds with hydrogen gas and a catalyst, the choice of palladium on carbon is able to hydrogenate alkenes and alkynes, but is unable to hydrogenate aromatic ...
13
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1answer
405 views

Is it possible to make an anticatalyst?

I'm wondering if it is possible, theoretically, to create compounds which perform the opposite function of a catalyst (thus an anticatalyst). That is to say, could a compound be made which raises the ...
13
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3answers
2k views

A misunderstanding about the energy profile of reactions with a catalyst involved

All of us are aware of the importance of the catalysts in bio-chemistry. For a high school learner like me, catalysts ,and therefore, enzymes play a bridge-like role that connect high school bio to ...
13
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1answer
366 views

What is the meaning of writing a catalyst name with two compounds split by a hyphen?

In literature, sometimes I see catalysts written with "-" between elements/compounds. Does this mean the first element/compound is supported on the second, or is the second a promoter? (e.g. $\ce{Fe}$-...
12
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4answers
11k views

Is there a catalyst that will reduce an alcohol to an alkane?

There are many reduction methods of going from an alcohol to an alkane: http://www.transtutors.com/chemistry-homework-help/hydrocarbons/reduction-of-alcohols.aspx And there are catalytic methods of ...
12
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3answers
2k views

What is the chemical formula of KIT-6?

I have seen KIT-6 used in literature as a catalyst support, but cannot find the chemical formula for it.
12
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1answer
14k views

Difference between nickel catalyst and Raney nickel catalyst

Many times I have seen the catalyst as Raney nickel instead of nickel catalyst. Raney nickel catalyst is developed by Murray Raney, and I think Raney nickel catalyst and nickel catalyst are two ...
12
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1answer
307 views

What might serve as an initial starting photocatalyst for this large water-splitting solar simulator?

Question: What might serve as an initial starting photocatalyst for this large water-splitting solar simulator? Surely there must have been some planned experiments! The Gizmodo article Insane Light ...
11
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4answers
389 views

What is an example of chemical reaction that can be assisted by both an inorganic catalyst and an enzyme?

I have been researching chemical reactions of inorganic catalysts and enzymes and cannot find a chemical process where an inorganic compound can be replaced by an enzyme (or vice versa) and have the ...
11
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2answers
11k views

Reaction intermediates of MnO2 catalyzed H2O2 decomposition reaction

Manganese dioxide catalyzes the decomposition of hydrogen peroxide to water and oxygen gas. But what are the intermediates in this catalyzed reaction?
11
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1answer
681 views

Stability of transition and post-transition metal alkoxides

Many transition metal alkoxides are seen in chemistry, for instance those of $\ce{Ti, Sn}$ and $\ce{Al}$, and in particular one of those of aluminium has its own role in the MPV reduction reaction. I ...
11
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1answer
416 views

Terminal Alkyne in Suzuki Coupling

I've done a very similar reaction to the one below but by TLC I observe only starting materials. It's super clear that nothing else is going on. Conditions: K3PO4, Pd(dppf)Cl2, dioxane/water, heat to ...
10
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3answers
2k views

Why is more of a catalyst added, when it is not consumed?

… catalysis, the acceleration of chemical reactions by substances not consumed in the reactions themselves—substances known as catalysts. (Source) Now as I’ve understood, to keep a reaction going, ...
10
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1answer
133 views

How does the work that won the 2012 Sustainable Chemistry Award contribute to sustainable chemistry?

I'm seeking a lay explanation for how the work of Dr Marc Taillefer that won the 2012 European Sustainable Chemistry Award, contributes to sustainable chemistry. From the press release, Dr. Taillefer ...
9
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4answers
6k views

Does a catalyst increase atom economy?

Somebody I know insists that the use of a catalyst increases the atom economy. They did chemistry at school and were told that a catalyst increases the atom economy. He pointed me to several past ...
9
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1answer
4k views

How exactly does the oxidation of TEMPO by NaOCl/KBr work?

I would like to understand the exact process by which TEMPO is oxidized to the nitrosonium cation by NaOCl, as in the part of the mechanism shown in the diagram (1) surrounded by the red box: The ...
9
votes
1answer
254 views

Transition state optimisation on the surface of periclase

I want to model a reaction catalysed by periclase ($\ce{MgO}$) using DFT. I have a good guess on the transition state (TS) of the reaction that goes in gas phase/solvent (produced using MOPAC). The ...
9
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2answers
8k views

How can a catalyst not be included in a rate equation if, by definition, it speeds up a chemical reaction?

I thought that anything not in a rate equation was automatically zeroth order and therefore did not affect the reaction. However, I have heard that catalysts can be involved in a reaction while not ...
8
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3answers
3k views

How can water catalyse a reaction between iodine and aluminium?

A few drops of water can initiate a reaction between iodine and aluminium. https://www.youtube.com/watch?v=SKSU72-1ERc How can this happen, since iodine is only slightly soluble in water?
8
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1answer
1k views

Catalysist activation energy - the Brønsted-Evans-Polanyi relation

I have stumbled upon something called the Brønsted-Evans-Polanyi relation in a study about the design of catalysts (for reactions like those in hydrocracking fuel production.) The relation shows that ...
8
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1answer
4k views

What is an active centre of a catalyst?

I was studying catalytic poisoning and read that in temporary poisoning, the poisoners are held at active centres by weak forces. What is an 'active centre' in this context?
8
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2answers
672 views

Why aren't chaperones considered catalysts?

I'm reading about protein folding on Wikipedia and I stumbled on a bit about a class of proteins called chaperones that aid in the folding of proteins by: ...reducing possible unwanted aggregations ...
8
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2answers
211 views

Regioselectivity in Carbometallation

I am a student of organic chemistry and I frequently watch online open course lectures by various professors around the globe. Of these, in https://www.youtube.com/watch?v=OYAMls5x4EI, at about 27:10, ...
8
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1answer
13k views

Isomerisation of alkanes under Lewis acidic conditions

My textbook says: n-Alkanes on heating in the presence of anhydrous aluminium chloride and hydrogen chloride gas isomerise to branched chain alkanes. But no mechanism is given. After a little ...
7
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1answer
5k views

Why do we need acid when making acetone peroxide?

Acetone peroxide is a very dangerous explosive, easily detonated by mild heating, friction or shock. It appears in the form of small white crystals. This compound forms from the mixture of hydrogen ...
7
votes
1answer
237 views

Ozone catalysis

I know that catalysts don't change chemical equilibrium because they accelerate both the reactions in the same way. I can't understand why CFC catalysts accelerate ozone destruction but not ozone ...
7
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2answers
892 views

Would singlet oxygen in the engine cause a more efficient combustion?

Today someone told me about a new product — a mesh that is made from 5 different metals and when oxygen passes through it, singlet oxygen appears for a short period of time. This mesh needs to be ...
7
votes
1answer
9k views

How does a catalyst affect the rate equation?

If I determine the order of the reactants in a reaction without using a catalyst, and then use a catalyst, will the order of the reactants then be different?
7
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1answer
127 views

Multiple "/" in catalysts

What does it mean if a catalyst has multiple "/" symbols, such as $\ce{Mn/Fe/Al2O3}$? Does it mean either $\ce{Mn}$ or $\ce{Fe}$, or does it mean both are supported on $\ce{Al2O3}$?
7
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2answers
10k views

Demonstrating decomposition of hydrogen peroxide using iron(III) nitrate catalyst

I need a way to prove/show that hydrogen peroxide was decomposed through use of catalyst. I want to ensure that my catalyst: $\ce{Fe(NO3)3}$ or iron(III) nitrate is a catalyst, not a reactant/ ...
7
votes
2answers
7k views

Why are hydrogenation reactions exothermic?

I learned that all reactions that yield hydrogen are endothermic (such has reforming) and reactions that use up hydrogen are exothermic (FCC cracking, hydrogenation, etc.). But why is this so? I know ...
7
votes
1answer
2k views

Catalytic iodine in synthesis of phosphonium salts

From Clayden et al. However, iodine is expensive and a way round that problem is to use a catalytic amount of iodide. The next phosphonium salt is formed slowly from benzyl bromide but the ...
7
votes
1answer
213 views

Different chemoselectivity of transition metals in catalytic hydrogenation

I am quoting my Clayden et al 2nd edition: Some catalysts are particularly selective towards certain classes of compound – for example, Pt, Rh and Ru will selectively hydrogenate aromatic ...
7
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1answer
106 views

How can subtilisin still function without its catalytic triad?

I read chapter 9 in the book Biochemistry (5th edition), by Berg, Tymoczko, and Stryer (provided in the NCBI site here). It describes the mechanism of action of the chymotrypsin enzyme. The catalysis ...
7
votes
1answer
5k views

Why does NaOH catalyze H2O2 decomposition? [duplicate]

I had a lab practice in which I had to test the effectiveness of different catalysts for the decomposition of $\ce{H2O2}$. Among them, there was: $\ce{KI(aq)}$, $\ce{FeCl3(aq)}$, $\ce{MnO(s)}$, $\ce{...
7
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1answer
729 views

The Propinquity Effect

I am currently in the process of studying enzyme catalysis and am struggling to get to grips with this concept. As far as I understand, the propinquity effect allows substrates to bind with enzymes in ...
7
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0answers
92 views

Why do poisoned catalysts (Lindlar, nickel borate) result in partial hydrogenation of alkynes?

I read that alkene is more reactive than alkyne, so in hydrogenation of alkynes, it's difficult to isolate the alkenes. But with poisoned catalysts like Lindlar's catalyst or Nickel-Boron (Ni2B), they ...
6
votes
2answers
709 views

How do I heat my borosilicate reflux column?

I am gonna use a ceramic tape heater, but cannot wrap it around evenly. Is the glass column gonna be okay? I am running some tests on plastic pyrolysis. I am using the reflux condenser to make the ...
6
votes
2answers
129 views

What is 'coprecipitated (Ni,Fe)S'?

I am writing an essay on the origin of life and I was reading an article on hydrothermal vents. (Peptides by Activation of Amino Acids with CO on (Ni,Fe)S Surfaces: Implications for the Origin of Life)...
6
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1answer
354 views

Why is the Jacobsen's catalyst with tert-Butyl groups a better catalyst for epoxidation?

In an experiment I synthesised the below Jacobsen's catalst: I used it to create styrene oxide through epoxidation. Chiral GC analysis showed that the enantiometric excess was lower compared to using ...
6
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1answer
2k views

How does salt and water promote corrosion?

I was always wondering why iron only rusts when it gets wet. I know that for example aluminium oxidises on its own on regular basis. I also heard many complains that salt used to remove snow from ...
6
votes
1answer
520 views

How can the trityl tetrafluoroborate function as a Lewis-acid catalyst

Trityl tetrafluoroborate is a reagent sometimes used in synthesis as a very mild Lewis acid catalyst, and recently I've been (unsuccessfully) using it in some protecting group chemistry. Several ...
6
votes
1answer
285 views

Specific reduction of certain functional groups

Consider the compound $\ce{Alkyl-(4 oxocyclopent-2-ene)carboxylate (A)}$. For example consider- Now consider the operations: $\ce{1. (A) + (i)BH3/THF (ii) H+}$ $\ce{2. (A) + H2/Pt}$ ...

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