Eu vou alimentar o gato.

Yes, you often can leave it out.

Portuguese is a pro-drop language, which means the subject pronoun is often omitted when the verb already makes the subject clear.

• Eu vou alimentar o gato.
• Vou alimentar o gato.

Both mean the same thing: I am going to feed the cat.

Including eu can add:

• emphasis
• clarity
• contrast with someone else

For example:

• Eu vou alimentar o gato, e você limpa a caixa.
  I’ll feed the cat, and you clean the litter box.

Vou alimentar is the very common Portuguese structure:

ir + infinitive

Here:

• vou = I go / I am going
• alimentar = to feed

Together, vou alimentar means:

• I am going to feed
• sometimes simply I will feed

This is one of the most common ways to talk about the near future in Brazilian Portuguese.

Examples:

• Vou sair. = I’m going to leave.
• Vou estudar. = I’m going to study.
• Vou alimentar o gato. = I’m going to feed the cat.

Yes. You could say:

• Eu alimentarei o gato.

That is the simple future.

However, in everyday Brazilian Portuguese, vou alimentar is usually more natural and more common in speech.

So:

• Eu vou alimentar o gato. = very common, natural
• Eu alimentarei o gato. = correct, but more formal or less conversational

A native speaker in Brazil will very often prefer vou + infinitive in normal conversation.

Because o gato means the cat.

• o = the for a singular masculine noun
• gato = cat

So:

• o gato = the cat
• um gato = a cat

In this sentence, o gato suggests a specific cat, probably one both speaker and listener know about.

Compare:

• Vou alimentar o gato. = I’m going to feed the cat.
• Vou alimentar um gato. = I’m going to feed a cat.

Because gato is a masculine noun.

In Portuguese singular definite articles:

• o = the for masculine nouns
• a = the for feminine nouns

Examples:

• o gato = the male cat or sometimes just the cat
• a gata = the female cat

So if you are talking about a female cat, you would say:

• Eu vou alimentar a gata.

It is correct, but in everyday speech it can sound a little more formal or neutral depending on context.

Alimentar means to feed / to nourish. It is absolutely grammatical and natural, but many Brazilians also commonly say things like:

• dar comida para o gato
• dar ração para o gato

Examples:

• Vou alimentar o gato. = correct, slightly more direct/formal-neutral
• Vou dar comida para o gato. = very natural in everyday speech
• Vou dar ração para o gato. = very natural if you mean pet food specifically

So alimentar is good to know, but you will also hear other expressions a lot.

Yes, it can be used for people too.

It broadly means to feed or to nourish, so it works with:

• animals
• people
• even abstract things in figurative language

Examples:

• Ela alimentou o bebê. = She fed the baby.
• Eles alimentam os animais. = They feed the animals.
• Isso alimenta a esperança. = That feeds hope.

For everyday situations with people, though, Portuguese may sometimes prefer other expressions depending on context, such as dar comida or simply talking about someone eating.

Yes, you can.

Both are natural:

• Eu vou alimentar o gato.
• Vou alimentar o gato.

The most basic order here is:

subject + verb + object

But since eu can be omitted, Vou alimentar o gato is extremely common.

You generally would not put o gato before the verb unless you are emphasizing it:

• O gato, eu vou alimentar agora.

That sounds marked or contrastive, not neutral.

You put não before the verb vou:

• Eu não vou alimentar o gato.

That means:

• I’m not going to feed the cat.

Pattern:

• Eu vou...
• Eu não vou...

Examples:

• Eu vou sair. = I’m going to leave.
• Eu não vou sair. = I’m not going to leave.

Yes, but the form may look a little different from what an English speaker expects.

A direct object pronoun for o gato can be o or lo, depending on the structure.

A common written/formal version is:

• Eu vou alimentá-lo.

This comes from:

• alimentar + o → alimentá-lo

This is correct, but in spoken Brazilian Portuguese, people often avoid this kind of clitic pronoun and prefer:

• Eu vou alimentar ele.

Grammatically traditional:

• Vou alimentá-lo.

Very common in spoken Brazilian Portuguese:

• Vou alimentar ele.

If you are learning standard grammar, know alimentá-lo. If you are listening to real conversation in Brazil, expect to hear alimentar ele a lot.

A simple approximate pronunciation is:

eh-ooh VOH ah-lee-mehn-TAR oo GAH-too

A few notes:

• eu often sounds roughly like eh-ooh said quickly
• vou rhymes roughly with English go without the final glide being too strong
• alimentar has stress on the last syllable: -tar
• gato has stress on ga

In natural speech, words connect smoothly, so:

• alimentar o may sound almost like alimentáro
• vou alimentar o gato flows together rather than sounding word-by-word

A more natural rhythm is:

• Eu vou alimentar o gato.
• stress mainly on vou, tar, and ga

Usually it suggests a future action that is planned, intended, or expected soon, but in real usage it can also simply mean I will feed the cat.

So vou + infinitive often covers both:

• I’m going to feed the cat
• I will feed the cat

The exact nuance depends on context.

For example:

• Daqui a pouco, vou alimentar o gato.
  In a little while, I’m going to feed the cat.
• Quando eu chegar em casa, vou alimentar o gato.
  When I get home, I’ll feed the cat.

So don’t think of it as only an immediate future. It is a very flexible and common future structure.